Add options for standard parameter for nvc and nvc++

fixes mesonbuild#13271

docs/markdown/snippets/nvc_now_support_setting_std.md

@@ -0,0 +1,6 @@
+## nvc and nvc++ now support setting std
+
+The following standards are available for nvc: c89, c90, c99, c11,
+c17, c18, gnu90, gnu89, gnu99, gnu11, gnu17, gnu18. For nvc++: 
+c++98, c++03, c++11, c++14, c++17, c++20, c++23, gnu++98, gnu++03,
+gnu++11, gnu++14, gnu++17, gnu++20

mesonbuild/compilers/c.py

@@ -361,6 +361,14 @@ def __init__(self, ccache: T.List[str], exelist: T.List[str], version: str, for_
                            info, linker=linker, full_version=full_version)
         PGICompiler.__init__(self)
 
+    def get_options(self) -> 'MutableKeyedOptionDictType':
+        opts = CCompiler.get_options(self)
+        cppstd_choices = ['c89', 'c90', 'c99', 'c11', 'c17', 'c18']
+        std_opt = opts[self.form_compileropt_key('std')]
+        assert isinstance(std_opt, options.UserStdOption), 'for mypy'
+        std_opt.set_versions(cppstd_choices, gnu=True)
+        return opts
+
 
 class ElbrusCCompiler(ElbrusCompiler, CCompiler):
     def __init__(self, ccache: T.List[str], exelist: T.List[str], version: str, for_machine: MachineChoice, is_cross: bool,

mesonbuild/compilers/cpp.py

@@ -566,6 +566,17 @@ def __init__(self, ccache: T.List[str], exelist: T.List[str], version: str, for_
                              info, linker=linker, full_version=full_version)
         PGICompiler.__init__(self)
 
+    def get_options(self) -> 'MutableKeyedOptionDictType':
+        opts = CPPCompiler.get_options(self)
+        cppstd_choices = [
+            'c++98', 'c++03', 'c++11', 'c++14', 'c++17', 'c++20', 'c++23',
+            'gnu++98', 'gnu++03', 'gnu++11', 'gnu++14', 'gnu++17', 'gnu++20'
+        ]
+        std_opt = opts[self.form_compileropt_key('std')]
+        assert isinstance(std_opt, options.UserStdOption), 'for mypy'
+        std_opt.set_versions(cppstd_choices)
+        return opts
+
 
 class ElbrusCPPCompiler(ElbrusCompiler, CPPCompiler):
     def __init__(self, ccache: T.List[str], exelist: T.List[str], version: str, for_machine: MachineChoice, is_cross: bool,