Introduce support for DJGPP cross compiler

DJGPP cross compiler is targeting DOS which does not support POSIX
signals. Probably for the same reason (targeting DOS) this compiler
does not support wide characters.

include/internal/catch_console_colour.cpp

@@ -169,7 +169,12 @@ namespace {
 #ifdef CATCH_PLATFORM_MAC
             !isDebuggerActive() &&
 #endif
-            isatty(STDOUT_FILENO);
+#if !(defined(__DJGPP__) && defined(__STRICT_ANSI__))
+            isatty(STDOUT_FILENO)
+#else
+            false
+#endif
+            ;
     }
     IColourImpl* platformColourInstance() {
         ErrnoGuard guard;