Bug 1511078: Follow-up - fix mingw build failures for TestNativeNt; r=bustage

mozglue/tests/TestNativeNt.cpp

@@ -38,7 +38,7 @@ const char kFailFmt[] =
 using namespace mozilla;
 using namespace mozilla::nt;
 
-extern "C" int wmain(int argc, wchar_t* argv[]) {
+int main(int argc, char* argv[]) {
   UNICODE_STRING normal;
   ::RtlInitUnicodeString(&normal, kNormal);