linkers: Fix detection of link arguments to Clang(-cl) + MSVC

Currently, not only Meson lacks a way to induce a "--fatal-warnings" on
LINK.exe, it is also unable to pass flags appropriately when using
clang-cl or Microsoft's stock clang.

This commit fixes it by implementing `fatal_warnings()` in the
MSVCDynamicLinker and ClangCLDynamicLinker classes, and by implementing
the requisite conversion steps in linker_to_compiler_args for
ClangCompiler.

mesonbuild/compilers/mixins/clang.py

@@ -11,7 +11,7 @@ import typing as T
 
 from ... import mesonlib
 from ...linkers.linkers import AppleDynamicLinker, ClangClDynamicLinker, LLVMDynamicLinker, GnuGoldDynamicLinker, \
-    MoldDynamicLinker
+    MoldDynamicLinker, MSVCDynamicLinker
 from ...mesonlib import OptionKey
 from ..compilers import CompileCheckMode
 from .gnu import GnuLikeCompiler
@@ -155,6 +155,12 @@ class ClangCompiler(GnuLikeCompiler):
             args.extend(super().get_lto_compile_args(threads=threads))
         return args
 
+    def linker_to_compiler_args(self, args: T.List[str]) -> T.List[str]:
+        if isinstance(self.linker, (ClangClDynamicLinker, MSVCDynamicLinker)):
+            return [flag if flag.startswith('-Wl,') else f'-Wl,{flag}' for flag in args]
+        else:
+            return args
+
     def get_lto_link_args(self, *, threads: int = 0, mode: str = 'default',
                           thinlto_cache_dir: T.Optional[str] = None) -> T.List[str]:
         args = self.get_lto_compile_args(threads=threads, mode=mode)

mesonbuild/linkers/linkers.py

@@ -1313,6 +1313,9 @@ class MSVCDynamicLinker(VisualStudioLikeLinkerMixin, DynamicLinker):
     def get_win_subsystem_args(self, value: str) -> T.List[str]:
         return self._apply_prefix([f'/SUBSYSTEM:{value.upper()}'])
 
+    def fatal_warnings(self) -> T.List[str]:
+        return ['-WX']
+
 
 class ClangClDynamicLinker(VisualStudioLikeLinkerMixin, DynamicLinker):
 
@@ -1342,6 +1345,9 @@ class ClangClDynamicLinker(VisualStudioLikeLinkerMixin, DynamicLinker):
     def get_thinlto_cache_args(self, path: str) -> T.List[str]:
         return ["/lldltocache:" + path]
 
+    def fatal_warnings(self) -> T.List[str]:
+        return ['-WX']
+
 
 class XilinkDynamicLinker(VisualStudioLikeLinkerMixin, DynamicLinker):