Revert "compilers/c++: Add MSVC option to make the __cplusplus define accurate"

This reverts commit 0b97d58548.

docs/markdown/snippets/msvc_cplusplus_define.md

@@ -1,7 +0,0 @@
-## MSVC now sets the __cplusplus #define accurately
-
-For reasons, MSVC will always return `199711L` for `__cplusplus`, even when a
-newer c++ standard is explicitly requested, unless you pass a specific option to
-the compiler for MSVC 2017 15.7 and newer. Older versions are unaffected by
-this. Meson now always sets the option if it is available, as it is unlikley
-that users want the default behavior.

mesonbuild/compilers/cpp.py

@@ -692,17 +692,6 @@ class VisualStudioCPPCompiler(CPP11AsCPP14Mixin, VisualStudioLikeCPPCompilerMixi
             del args[i]
         return args
 
-    def get_always_args(self) -> T.List[str]:
-        args = super().get_always_args()
-
-        # update the __cplusplus #define to match the version given on the
-        # command line with /std:NNN, but only for versions above 15.7 (2017)
-        # https://docs.microsoft.com/en-us/cpp/build/reference/zc-cplusplus?view=msvc-160
-        if version_compare(self.version, '>= 15.7'):
-            args.append('/Zc:__cplusplus')
-
-        return args
-
 class ClangClCPPCompiler(CPP11AsCPP14Mixin, VisualStudioLikeCPPCompilerMixin, ClangClCompiler, CPPCompiler):
     def __init__(self, exelist: T.List[str], version: str, for_machine: MachineChoice,
                  is_cross: bool, info: 'MachineInfo', target: str,

test cases/windows/18 msvc cplusplus define/main.cpp

@@ -1,7 +0,0 @@
-int main() {
-#if __cplusplus == 199711L
-    return 1;
-#else
-    return 0;
-#endif
-}

test cases/windows/18 msvc cplusplus define/meson.build

@@ -1,14 +0,0 @@
-project('msvc __cplusplus', 'cpp', default_options : ['cpp_std=c++14'])
-
-cpp = meson.get_compiler('cpp')
-
-if cpp.get_id() != 'msvc'
-  error('MESON_SKIP_TEST: test is only relavent for msvc')
-elif meson.project_version().version_compare('< 15.7')
-  error('MESON_SKIP_TEST: test is only relavent for msvc versions >= 15.7')
-endif
-
-test(
-  'main',
-  executable('main', 'main.cpp'),
-)

test cases/windows/3 cpp/meson.build

@@ -1,4 +1,4 @@
-project('wincpp', 'cpp', default_options : ['cpp_std=c++14'])
+project('wincpp', 'cpp')
 
 exe = executable('prog', 'prog.cpp')
 test('wincpp', exe)

unittests/windowstests.py

@@ -359,3 +359,4 @@ class WindowsTests(BasePlatformTests):
             raise SkipTest('C++ modules are only supported with VS 2019 Preview or newer.')
         self.init(os.path.join(self.unit_test_dir, '86 cpp modules'))
         self.build()
+