gl_renderer: print more GL ES feature flags

This is a human readable replacement for printing out the list of all
available GL extensions that doesn't happen anymore by default.

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.com>

shared/string-helpers.h

@@ -95,4 +95,10 @@ str_printf(char **str_out, const char *fmt, ...)
 		*str_out = NULL;
 }
 
+static inline const char *
+yesno(bool cond)
+{
+	return cond ? "yes" : "no";
+}
+
 #endif /* WESTON_STRING_HELPERS_H */