fix building _std_extensions.h with MinGW

Author: q4a

src/xrCore/_std_extensions.h

@@ -87,37 +87,43 @@ IC bool _valid(const float x) noexcept
 {
     // check for: Signaling NaN, Quiet NaN, Negative infinity ( ???INF), Positive infinity (+INF), Negative denormalized,
     // Positive denormalized
-#if defined(WINDOWS)
+#if defined(WINDOWS) && defined(_MSC_VER)
     int cls = _fpclass(double(x));
     if (cls & (_FPCLASS_SNAN + _FPCLASS_QNAN + _FPCLASS_NINF + _FPCLASS_PINF + _FPCLASS_ND + _FPCLASS_PD))
         return false;
-#endif
+#else
+    #pragma todo("Find Linux alternative for _fpclass. Check https://github.com/mirror/mingw-w64/blob/master/mingw-w64-headers/crt/math.h");
+
     /* *****other cases are*****
     _FPCLASS_NN Negative normalized non-zero
     _FPCLASS_NZ Negative zero ( ??? 0)
     _FPCLASS_PZ Positive 0 (+0)
     _FPCLASS_PN Positive normalized non-zero
     */
     return true;
+#endif
 }
 
 // double
 IC bool _valid(const double x)
 {
     // check for: Signaling NaN, Quiet NaN, Negative infinity ( ???INF), Positive infinity (+INF), Negative denormalized,
     // Positive denormalized
-#if defined(WINDOWS)
+#if defined(WINDOWS) && defined(_MSC_VER)
     int cls = _fpclass(x);
     if (cls & (_FPCLASS_SNAN + _FPCLASS_QNAN + _FPCLASS_NINF + _FPCLASS_PINF + _FPCLASS_ND + _FPCLASS_PD))
         return false;
-#endif
+#else
+    #pragma todo("Find Linux alternative for _fpclass. Check https://github.com/mirror/mingw-w64/blob/master/mingw-w64-headers/crt/math.h");
+
     /* *****other cases are*****
     _FPCLASS_NN Negative normalized non-zero
     _FPCLASS_NZ Negative zero ( ??? 0)
     _FPCLASS_PZ Positive 0 (+0)
     _FPCLASS_PN Positive normalized non-zero
     */
     return true;
+#endif
 }
 
 // XXX: "magic" specializations, that really require profiling to see if they are worth this effort.