Convert efree() to a macro that just casts to void * and does free().

If the system free() can't handle free(NULL) this may crash but C89
was a long time ago.

include/alloc.h

@@ -19,9 +19,11 @@
 
 #include <stdarg.h>
 
+#undef efree
+#define efree(x)	free((void *)(x))
+
 int	 easprintf(char **, const char *, ...) __printflike(2, 3);
 int	 evasprintf(char **, const char *, va_list) __printflike(2, 0);
-void	 efree(void *);
 void	*ecalloc(size_t, size_t) __malloc_like;
 void	*emalloc(size_t) __malloc_like;
 void	*emalloc2(size_t, size_t) __malloc_like;