Compile to C99 instead of GNU11

Simpler, now that we don't need the time structs anymore.

makefile

@@ -1,5 +1,5 @@
 xkbcat: xkbcat.c
-	clang -O3 --std=gnu11 -pedantic -Wall -lX11 -lXi -o xkbcat xkbcat.c
+	clang -O3 --std=c99 -pedantic -Wall -lX11 -lXi -o xkbcat xkbcat.c
 clean:
 	rm xkbcat
 .PHONY: xkbcat