fix zig cc to convert zig-triple → llvm-triple

[mikdusan]

• issue manifested when piping to zig cc -E -

---

• zig passed zig-triples when punting to clang, preprocessing and with piped input

• look for native in target strings below to see indicators of the bug

• BEFORE

! zig cc -E -v -target native-linux - < /dev/null
  
- Target: native-unknown-linux
  Thread model: posix
  InstalledDir: /usr/bin
   (in-process)
   "/home/mike/project/zig/work/main/_build/zig"
      -cc1
-     -triple native-unknown-linux
      -E
      -disable-free
      -disable-llvm-verifier
      -discard-value-names
      -main-file-name
      -
      -mrelocation-model static
      -mframe-pointer=all
      -fmath-errno
      -fno-rounding-math
      -fno-verbose-asm
      -no-integrated-as
      -mconstructor-aliases
      -fno-split-dwarf-inlining
      -debugger-tuning=gdb
      -v
      -resource-dir /home/mike/project/zig/work/main/lib/clang/11.0.1
      -internal-isystem /usr/local/include
      -internal-isystem /home/mike/project/zig/work/main/lib/clang/11.0.1/include
      -internal-externc-isystem /include
      -internal-externc-isystem /usr/include
      -fno-dwarf-directory-asm
      -fdebug-compilation-dir /home/mike/project/zig/work/main
      -ferror-limit 19
      -fgnuc-version=4.2.1
      -fcolor-diagnostics
      -o
      -
      -x c
      -
- error: unknown target triple 'native-unknown-linux', please use -triple or -arch

• AFTER

! zig cc -E -v -target native-linux - < /dev/null
  
+ Target: x86_64-unknown-linux-musl
  Thread model: posix
  InstalledDir: /usr/bin
   (in-process)
   "/home/mike/project/zig/work/zigcc/_build/zig"
      -cc1
+     -triple x86_64-unknown-linux-musl
      -E
      -disable-free
      -disable-llvm-verifier
      -discard-value-names
      -main-file-name
      -
      -mrelocation-model pic
      -pic-level 2
      -pic-is-pie
      -mframe-pointer=all
      -fmath-errno
      -fno-rounding-math
      -mconstructor-aliases
      -munwind-tables
      -target-cpu x86-64
      -fno-split-dwarf-inlining
      -debugger-tuning=gdb
      -v
      -resource-dir /home/mike/project/zig/work/zigcc/lib/clang/11.0.1
      -internal-isystem /usr/local/include
      -internal-externc-isystem /include
      -internal-externc-isystem /usr/include
      -internal-isystem /home/mike/project/zig/work/zigcc/lib/clang/11.0.1/include
      -fdebug-compilation-dir /home/mike/project/zig/work/zigcc
      -ferror-limit 19
      -fgnuc-version=4.2.1
      -fcolor-diagnostics
      -faddrsig
      -o
      -
      -x c
      -
+ # 1 "<stdin>"
+ # 1 "<built-in>" 1
+ # 1 "<built-in>" 3
+ # 345 "<built-in>" 3
+ # 1 "<command line>" 1
+ # 1 "<built-in>" 2
+ # 1 "<stdin>" 2

[LemonBoy]

#7360 is somewhat related and relatively straightforward to fix once we decide how to handle that.

[mikdusan]

after talking with andrew, going to rework PR with new approach:

• consider piped-input preprocessor the same as having 1 source file and avoid punt_to_clang() altogether
• adjust rest of fn body to handle accordingly

[andrewrk]

30+ days old draft; closing