cygwinccompiler: Get the compilers from sysconfig

On the CLANG64 environment of MSYS2, we should use clang
instead of gcc. This patch gets the compiler from sysconfig which
would be set when Python was built.

Without this patch, the build fails when it's trying to check if the
compiler is cygwin's one.

distutils/cygwinccompiler.py

@@ -21,6 +21,7 @@
     DistutilsPlatformError,
 )
 from .file_util import write_file
+from .sysconfig import get_config_vars
 from .unixccompiler import UnixCCompiler
 from .version import LooseVersion, suppress_known_deprecation
 
@@ -61,8 +62,12 @@ def __init__(self, verbose=False, dry_run=False, force=False):
                 "Compiling may fail because of undefined preprocessor macros."
             )
 
-        self.cc = os.environ.get('CC', 'gcc')
-        self.cxx = os.environ.get('CXX', 'g++')
+        self.cc, self.cxx = get_config_vars('CC', 'CXX')
+
+        # Override 'CC' and 'CXX' environment variables for
+        # building using MINGW compiler for MSVC python.
+        self.cc = os.environ.get('CC', self.cc or 'gcc')
+        self.cxx = os.environ.get('CXX', self.cxx or 'g++')
 
         self.linker_dll = self.cc
         self.linker_dll_cxx = self.cxx