[Fix] Linking error on some platforms using VS2015.

Fixes issue #454. Credits to @fangguanya for the fix.

src/Win32_Interop/win32fixes.h

@@ -55,12 +55,21 @@
 #endif
 #endif
 
+#ifdef __cplusplus
+extern "C"
+{
+#endif
+
 /* strtod does not handle Inf and Nan, we need to do the check before calling strtod */
 #undef strtod
 #define strtod(nptr, eptr) wstrtod((nptr), (eptr))
 
 double wstrtod(const char *nptr, char **eptr);
 
+#ifdef __cplusplus
+}
+#endif
+
 // access check for executable uses X_OK. For Windows use READ access.
 #ifndef X_OK
 #define X_OK 4