Use std::isfinite() for wxFinite() for C++11 compilers.

This should fix compilation with MinGW 4.8.1 cross-compiler in C++11 mode as
it doesn't seem to provide finite() any more then.

Also, only defined wxFinite() and wxIsNaN() for C++, not C. This makes the
checks for __cplusplus >= 201103 simpler and is consistent with how
wxIsSameDouble() and wxRound() were already only defined for C++ (this is also
the source of most of the changes in this diff, viewing it ignoring whitespace
will show the only real changes).

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@74837 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/math.h

@@ -51,9 +51,13 @@
 #endif
 
 
-/* unknown __VISAGECC__, __SYMANTECCC__ */
+#ifdef __cplusplus
 
-#if defined(__VISUALC__) || defined(__BORLANDC__) || defined(__WATCOMC__)
+/* Any C++11 compiler should provide isfinite() */
+#if __cplusplus >= 201103
+    #include <cmath>
+    #define wxFinite(x) std::isfinite(x)
+#elif defined(__VISUALC__) || defined(__BORLANDC__) || defined(__WATCOMC__)
     #include <float.h>
     #define wxFinite(x) _finite(x)
 #elif defined(__MINGW64__) || defined(__clang__)
@@ -89,8 +93,6 @@
     #define wxIsNaN(x) ((x) != (x))
 #endif
 
-#ifdef __cplusplus
-
 #ifdef __INTELC__
 
     inline bool wxIsSameDouble(double x, double y)
@@ -130,6 +132,7 @@
         return (int)(x < 0 ? x - 0.5 : x + 0.5);
     #endif
 }
+
 #endif /* __cplusplus */