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/peachwm.c

@@ -4003,6 +4003,7 @@ int main(int argc, char *argv[]) {
       break;
     case 'v':
       die("peachwm " VERSION);
+      break;
     default:
       goto usage;
     }

src/util.c

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

src/util.h

@@ -1,5 +1,5 @@
 /* See LICENSE.dwm file for copyright and license details. */
 
-void die(const char *fmt, ...);
+_Noreturn void die(const char *fmt, ...);
 void *ecalloc(size_t nmemb, size_t size);
 int fd_set_nonblock(int fd);