Windows follow-up: minimize pragma scope

Avoid disruption to mingw32-x64 build, by placing
some Visual Studio pragmas in #ifdef _MSC_VER
conditional blocks.

sys/windows/windsys.c

@@ -627,10 +627,14 @@ BOOL winos_font_support_cp437(HFONT hFont)
     if (size) {
         GLYPHSET *glyphSet = (GLYPHSET *) malloc((size_t) size);
         if (glyphSet != NULL) {
+#ifdef _MSC_VER
 #pragma warning( push )
 #pragma warning( disable : 6386 )
+#endif
             size = GetFontUnicodeRanges(hdc, glyphSet);
+#ifdef _MSC_VER
 #pragma warning( pop )
+#endif
             allFound = TRUE;
             for (int i = 0; i < 256 && allFound; i++) {
                 WCHAR wc = cp437[i];

win/win32/NetHackW.c

@@ -77,8 +77,11 @@ static void __cdecl mswin_moveloop(void *);
 
 #define MAX_CMDLINE_PARAM 255
 
+#ifdef _MSC_VER
 #pragma warning( push )
 #pragma warning( disable : 28251)
+#endif
+
 int APIENTRY
 WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine,
         int nCmdShow)
@@ -248,7 +251,9 @@ WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine,
     return 0;
 }
 
+#ifdef _MSC_VER
 #pragma warning( pop )
+#endif
 
 PNHWinApp
 GetNHApp(void)