Add features to Makefile

make release - compiles with clang, uses more aggressive compilation
flags for errors/warnings.
CC=tcc/gcc/clang make - lets you select your wanted compiler.

src/util.c

@@ -7,7 +7,7 @@
 
 #include "util.h"
 
-void
+_Noreturn void
 die(const char *fmt, ...) {
 	va_list ap;