compilers: add c23 and gnu23 c_stds

Closes: https://github.com/mesonbuild/meson/issues/12702

docs/markdown/Builtin-options.md

@@ -257,7 +257,7 @@ or compiler being used:
 | ------           | ------------- | ---------------                          | ----------- |
 | c_args           |               | free-form comma-separated list           | C compile arguments to use |
 | c_link_args      |               | free-form comma-separated list           | C link arguments to use |
-| c_std            | none          | none, c89, c99, c11, c17, c18, c2x, gnu89, gnu99, gnu11, gnu17, gnu18, gnu2x | C language standard to use |
+| c_std            | none          | none, c89, c99, c11, c17, c18, c2x, c23, gnu89, gnu99, gnu11, gnu17, gnu18, gnu2x, gnu23 | C language standard to use |
 | c_winlibs        | see below     | free-form comma-separated list           | Standard Windows libs to link against |
 | c_thread_count   | 4             | integer value ≥ 0                        | Number of threads to use with emcc when using threads |
 | cpp_args         |               | free-form comma-separated list           | C++ compile arguments to use |

docs/markdown/Configuring-a-build-directory.md

@@ -61,7 +61,7 @@ a sample output for a simple project.
       ------        ------------- ---------------                                                                                               -----------
       c_args        []                                                                                                                          Extra arguments passed to the C compiler
       c_link_args   []                                                                                                                          Extra arguments passed to the C linker
-      c_std         c99           [none, c89, c99, c11, c17, c18, c2x, gnu89, gnu99, gnu11, gnu17, gnu18, gnu2x]                                C language standard to use
+      c_std         c99           [none, c89, c99, c11, c17, c18, c2x, c23, gnu89, gnu99, gnu11, gnu17, gnu18, gnu2x, gnu23]                                C language standard to use
       cpp_args      []                                                                                                                          Extra arguments passed to the C++ compiler
       cpp_debugstl  false         [true, false]                                                                                                 STL debug mode
       cpp_link_args []                                                                                                                          Extra arguments passed to the C++ linker

mesonbuild/compilers/c.py

@@ -46,7 +46,7 @@ if T.TYPE_CHECKING:
 else:
     CompilerMixinBase = object
 
-_ALL_STDS = ['c89', 'c9x', 'c90', 'c99', 'c1x', 'c11', 'c17', 'c18', 'c2x']
+_ALL_STDS = ['c89', 'c9x', 'c90', 'c99', 'c1x', 'c11', 'c17', 'c18', 'c2x', 'c23']
 _ALL_STDS += [f'gnu{std[1:]}' for std in _ALL_STDS]
 _ALL_STDS += ['iso9899:1990', 'iso9899:199409', 'iso9899:1999', 'iso9899:2011', 'iso9899:2017', 'iso9899:2018']
 
@@ -113,6 +113,7 @@ class _ClangCStds(CompilerMixinBase):
     _C17_VERSION = '>=6.0.0'
     _C18_VERSION = '>=8.0.0'
     _C2X_VERSION = '>=9.0.0'
+    _C23_VERSION = '>=18.0.0'
 
     def get_options(self) -> 'MutableKeyedOptionDictType':
         opts = super().get_options()
@@ -125,6 +126,8 @@ class _ClangCStds(CompilerMixinBase):
             stds += ['c18']
         if version_compare(self.version, self._C2X_VERSION):
             stds += ['c2x']
+        if version_compare(self.version, self._C23_VERSION):
+            stds += ['c23']
         std_opt = opts[OptionKey('std', machine=self.for_machine, lang=self.language)]
         assert isinstance(std_opt, coredata.UserStdOption), 'for mypy'
         std_opt.set_versions(stds, gnu=True)
@@ -253,6 +256,7 @@ class GnuCCompiler(GnuCompiler, CCompiler):
 
     _C18_VERSION = '>=8.0.0'
     _C2X_VERSION = '>=9.0.0'
+    _C23_VERSION = '>=14.0.0'
     _INVALID_PCH_VERSION = ">=3.4.0"
 
     def __init__(self, ccache: T.List[str], exelist: T.List[str], version: str, for_machine: MachineChoice, is_cross: bool,
@@ -280,6 +284,8 @@ class GnuCCompiler(GnuCompiler, CCompiler):
             stds += ['c17', 'c18']
         if version_compare(self.version, self._C2X_VERSION):
             stds += ['c2x']
+        if version_compare(self.version, self._C23_VERSION):
+            stds += ['c23']
         key = OptionKey('std', machine=self.for_machine, lang=self.language)
         std_opt = opts[key]
         assert isinstance(std_opt, coredata.UserStdOption), 'for mypy'