dependencies: Always convert MinGW paths to MSVC on Windows

The MinGW toolchain can read MinGW paths, but Python cannot and we
sometimes need to parse the libs and cflags manually (for static-only
library searching, for instance). The MinGW toolchain can always read
Windows paths with `/` as path separater, so just use that.

mesonbuild/dependencies/base.py

@@ -414,11 +414,12 @@ class PkgConfigDependency(ExternalDependency):
 
     def _convert_mingw_paths(self, args):
         '''
-        MSVC cannot handle MinGW-esque /c/foo paths, convert them to C:/foo.
+        Both MSVC and native Python on Windows cannot handle MinGW-esque /c/foo
-        We cannot resolve other paths starting with / like /home/foo so leave
+        paths so convert them to C:/foo. We cannot resolve other paths starting
-        them as-is so the user gets an error/warning from the compiler/linker.
+        with / like /home/foo so leave them as-is so that the user gets an
+        error/warning from the compiler/linker.
         '''
-        if not self.compiler or self.compiler.id != 'msvc':
+        if not mesonlib.is_windows():
             return args
         converted = []
         for arg in args: