docs: update minimum GCC version (#14431)

CMakeLists.txt

@@ -30,9 +30,9 @@ if (NOT "${PROJECT_VERSION_PRE_RELEASE}" STREQUAL "")
 endif ()
 
 if ("${CMAKE_CXX_COMPILER_ID}" STREQUAL "GNU")
-    if (CMAKE_CXX_COMPILER_VERSION VERSION_LESS 7.3)
+    if (CMAKE_CXX_COMPILER_VERSION VERSION_LESS 7.5)
         message(
-            WARNING "The `google-cloud-cpp` library is tested with GCC >= 7.3."
+            WARNING "The `google-cloud-cpp` library is tested with GCC >= 7.5."
                     " We will consider patches for older versions.")
     endif ()
 elseif ("${CMAKE_CXX_COMPILER_ID}" STREQUAL "Clang")

README.md

@@ -546,7 +546,7 @@ The binary artifacts, such as examples, will be placed in `cmake-out/`.
   - Language Version (>= C++14).
   - Operating Systems: Windows, macOS, and Linux.
   - Build Systems: Bazel (>= 6.0), CMake (>= 3.10).
-  - Compilers: GCC (>= 7.3), Clang (>= 6.0), MSVC (>= 2022), Apple Clang (>=
+  - Compilers: GCC (>= 7.5), Clang (>= 6.0), MSVC (>= 2022), Apple Clang (>=
     12).
 - This project uses dependencies described in
   [doc/packaging.md](https://github.com/googleapis/google-cloud-cpp/blob/main/doc/packaging.md).

google/cloud/README.md

@@ -18,8 +18,8 @@ notice. These include `google/cloud/internal/`, and
 ## Supported Platforms
 
 - Windows, macOS, Linux
-- C++14 (and higher) compilers (we test with GCC >= 7.3, Clang >= 6.0, and MSVC
-  \>= 2022)
+- C++14 (and higher) compilers. We test with GCC >= 7.5, Clang >= 6.0, and MSVC
+  \>= 2022
 - Environments with or without exceptions
 - Bazel (>= 6.0) and CMake (>= 3.5) builds
 

google/cloud/storage/google_cloud_cpp_storage.cmake

@@ -290,12 +290,10 @@ target_include_directories(
 target_compile_options(google_cloud_cpp_storage
                        PUBLIC ${GOOGLE_CLOUD_CPP_EXCEPTIONS_FLAG})
 
-# GCC-7.3 (the default GCC version on Ubuntu:18.04) issues a warning (a member
-# variable may be used without being initialized), in this file. GCC-8.0 no
-# longer emits that diagnostic, and neither does Clang. On the assumption that
-# this is a spurious warning we disable it for older versions of GCC. I (coryan)
-# did not research in exactly what version was this warning introduced, and when
-# it was fixed. I do not believe we need to be that accurate.
+# GCC-7.x issues a warning (a member variable may be used without being
+# initialized), in this file. GCC-8.0 no longer emits that diagnostic, and
+# neither does Clang. On the assumption that this is a spurious warning we
+# disable it for older versions of GCC.
 if (${CMAKE_CXX_COMPILER_ID} STREQUAL "GNU" AND ${CMAKE_CXX_COMPILER_VERSION}
                                                 VERSION_LESS 8.0)
     set_property(