vdisp/gl: FEATURE_PRESENT simplified

strcmp not actually required, just compare first char (1 or '\0')

Mentioned by CID 899145 (pointless comparison, after preprocesor
expansion) but most likely won't fix that (but doesn't need to be fixed,
anyways).

Author: MartinPulec

src/video_display/gl.cpp

@@ -572,7 +572,7 @@ gl_print_current_platform()
 }
 #endif // not defined GLFW_PLATFORM
 
-#define FEATURE_PRESENT(x) (strcmp(STRINGIFY(x), "1") == 0 ? "on" : "off")
+#define FEATURE_PRESENT(x) (STRINGIFY(x)[0] == 1 ? "on" : "off")
 
 /**
  * Show help