Enable consteval for Xcode 14 and later

[cloyce]

The consteval problems that affected clang from Xcode 13 and earlier have been fixed in Xcode 14. This patch just makes the Xcode exclusion a little more targeted.

Tested on an Apple Silicon Mac running macOS 13.2 with Xcode 14.0.1, Xcode 14.2.0, Xcode 14.3 beta, and some later internal builds. I did actually also test with Xcode 13.4, and it was fine, but that's not a supported config so I'm not going to officially claim it works. 😄

Build (including with FMT_PEDANTIC) and tests all pass, both in C++11 and C++20 modes. (The default is C++98, so not setting CMAKE_CXX_STANDARD really isn't an option.)

C++11 (make && make test):

-- CMake version: 3.25.2
-- The CXX compiler identification is AppleClang 14.0.0.14000029
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: /Applications/Xcode-14A.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/c++ - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Module support is disabled.
-- Version: 9.1.1
-- Build type: Release
-- Performing Test HAS_NULLPTR_WARNING
-- Performing Test HAS_NULLPTR_WARNING - Success
-- Target 'doc' disabled (requires doxygen)
-- Performing Test CMAKE_HAVE_LIBC_PTHREAD
-- Performing Test CMAKE_HAVE_LIBC_PTHREAD - Success
-- Found Threads: TRUE  
-- Looking for strptime
-- Looking for strptime - found
-- FMT_PEDANTIC: ON
-- Performing Test HAVE_FNO_EXCEPTIONS_FLAG
-- Performing Test HAVE_FNO_EXCEPTIONS_FLAG - Success
-- Configuring done
-- Generating done
-- Build files have been written to: /Users/cloyce/src-ext/fmt-cds/b14A-11
[...]
Running tests...
Test project /Users/cloyce/src-ext/fmt-cds/b14A-11
      Start  1: args-test
 1/24 Test  #1: args-test ........................   Passed    0.00 sec
      Start  2: assert-test
 2/24 Test  #2: assert-test ......................   Passed    0.00 sec
      Start  3: chrono-test
 3/24 Test  #3: chrono-test ......................   Passed    0.03 sec
      Start  4: color-test
 4/24 Test  #4: color-test .......................   Passed    0.00 sec
      Start  5: core-test
 5/24 Test  #5: core-test ........................   Passed    0.00 sec
      Start  6: gtest-extra-test
 6/24 Test  #6: gtest-extra-test .................   Passed    0.00 sec
      Start  7: format-test
 7/24 Test  #7: format-test ......................   Passed    0.01 sec
      Start  8: format-impl-test
 8/24 Test  #8: format-impl-test .................   Passed    0.02 sec
      Start  9: ostream-test
 9/24 Test  #9: ostream-test .....................   Passed    0.01 sec
      Start 10: compile-test
10/24 Test #10: compile-test .....................   Passed    0.00 sec
      Start 11: compile-fp-test
11/24 Test #11: compile-fp-test ..................   Passed    0.00 sec
      Start 12: printf-test
12/24 Test #12: printf-test ......................   Passed    0.00 sec
      Start 13: ranges-test
13/24 Test #13: ranges-test ......................   Passed    0.01 sec
      Start 14: scan-test
14/24 Test #14: scan-test ........................   Passed    0.00 sec
      Start 15: std-test
15/24 Test #15: std-test .........................   Passed    0.00 sec
      Start 16: unicode-test
16/24 Test #16: unicode-test .....................   Passed    0.00 sec
      Start 17: xchar-test
17/24 Test #17: xchar-test .......................   Passed    0.00 sec
      Start 18: enforce-checks-test
18/24 Test #18: enforce-checks-test ..............   Passed    0.00 sec
      Start 19: posix-mock-test
19/24 Test #19: posix-mock-test ..................   Passed    0.00 sec
      Start 20: os-test
20/24 Test #20: os-test ..........................   Passed    0.00 sec
      Start 21: compile-error-test
21/24 Test #21: compile-error-test ...............   Passed    5.42 sec
      Start 22: find-package-test
22/24 Test #22: find-package-test ................   Passed    2.46 sec
      Start 23: add-subdirectory-test
23/24 Test #23: add-subdirectory-test ............   Passed    3.85 sec
      Start 24: static-export-test
24/24 Test #24: static-export-test ...............   Passed    7.25 sec

100% tests passed, 0 tests failed out of 24

Total Test time (real) =  19.13 sec

C++20 (make && make test):

-- CMake version: 3.25.2
-- The CXX compiler identification is AppleClang 14.0.0.14000029
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: /Applications/Xcode-14A.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/c++ - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Version: 9.1.1
-- Build type: Release
-- Performing Test HAS_NULLPTR_WARNING
-- Performing Test HAS_NULLPTR_WARNING - Success
-- Target 'doc' disabled (requires doxygen)
-- Performing Test CMAKE_HAVE_LIBC_PTHREAD
-- Performing Test CMAKE_HAVE_LIBC_PTHREAD - Success
-- Found Threads: TRUE  
-- Looking for strptime
-- Looking for strptime - found
-- FMT_PEDANTIC: ON
-- Performing Test HAVE_FNO_EXCEPTIONS_FLAG
-- Performing Test HAVE_FNO_EXCEPTIONS_FLAG - Success
-- Configuring done
-- Generating done
-- Build files have been written to: /Users/cloyce/src-ext/fmt-cds/b14A-20
[...]
Running tests...
Test project /Users/cloyce/src-ext/fmt-cds/b14A-20
      Start  1: args-test
 1/24 Test  #1: args-test ........................   Passed    0.01 sec
      Start  2: assert-test
 2/24 Test  #2: assert-test ......................   Passed    0.01 sec
      Start  3: chrono-test
 3/24 Test  #3: chrono-test ......................   Passed    0.06 sec
      Start  4: color-test
 4/24 Test  #4: color-test .......................   Passed    0.01 sec
      Start  5: core-test
 5/24 Test  #5: core-test ........................   Passed    0.02 sec
      Start  6: gtest-extra-test
 6/24 Test  #6: gtest-extra-test .................   Passed    0.01 sec
      Start  7: format-test
 7/24 Test  #7: format-test ......................   Passed    0.03 sec
      Start  8: format-impl-test
 8/24 Test  #8: format-impl-test .................   Passed    0.03 sec
      Start  9: ostream-test
 9/24 Test  #9: ostream-test .....................   Passed    0.01 sec
      Start 10: compile-test
10/24 Test #10: compile-test .....................   Passed    0.01 sec
      Start 11: compile-fp-test
11/24 Test #11: compile-fp-test ..................   Passed    0.01 sec
      Start 12: printf-test
12/24 Test #12: printf-test ......................   Passed    0.00 sec
      Start 13: ranges-test
13/24 Test #13: ranges-test ......................   Passed    0.01 sec
      Start 14: scan-test
14/24 Test #14: scan-test ........................   Passed    0.01 sec
      Start 15: std-test
15/24 Test #15: std-test .........................   Passed    0.01 sec
      Start 16: unicode-test
16/24 Test #16: unicode-test .....................   Passed    0.02 sec
      Start 17: xchar-test
17/24 Test #17: xchar-test .......................   Passed    0.01 sec
      Start 18: enforce-checks-test
18/24 Test #18: enforce-checks-test ..............   Passed    0.01 sec
      Start 19: posix-mock-test
19/24 Test #19: posix-mock-test ..................   Passed    0.01 sec
      Start 20: os-test
20/24 Test #20: os-test ..........................   Passed    0.01 sec
      Start 21: compile-error-test
21/24 Test #21: compile-error-test ...............   Passed   17.37 sec
      Start 22: find-package-test
22/24 Test #22: find-package-test ................   Passed    2.35 sec
      Start 23: add-subdirectory-test
23/24 Test #23: add-subdirectory-test ............   Passed    4.10 sec
      Start 24: static-export-test
24/24 Test #24: static-export-test ...............   Passed    2.98 sec

100% tests passed, 0 tests failed out of 24

Total Test time (real) =  27.16 sec

Building the fuzzers fails in C++20 mode, but I also observed that on LLVM 14 on Linux/x86, so I don't consider that a regression.

[vitaut]

Thanks for the PR. LGTM but please apply clang-format to your changes.

[cloyce]

Thanks; I have done. I also fixed the conditional (>= vs >) which would've inadvertently excluded 14.0.1 (but nothing later I think). The version I tested had parens in the wrong place so there was effectively no Xcode exclusion. I fixed that before submitting the PR, but the tests I did are still valid. (I did re-do the checks on the previous version, just not with 5 versions of Xcode.)