Add declarations to fix the build with MinGW 5.3.0 in C++11 mode

Fix the build with -std=c++11 (instead of -std=gnu++11) by providing even
more declarations for the functions wrongly excluded from MinGW headers in
"strict ANSI" mode ourselves.

include/wx/wxcrtbase.h

@@ -194,6 +194,9 @@ extern unsigned long android_wcstoul(const wchar_t *nptr, wchar_t **endptr, int
     #endif
 
     #ifdef HAVE_STRTOULL
+        wxDECL_FOR_STRICT_MINGW32(long long, strtoll, (const char*, char**, int))
+        wxDECL_FOR_STRICT_MINGW32(unsigned long long, strtoull, (const char*, char**, int))
+
         #define wxCRT_StrtollA   strtoll
         #define wxCRT_StrtoullA  strtoull
     #endif /* HAVE_STRTOULL */