Use a smaller size for the lexer buffer

Large sizes are more efficient when it's actually buffered,
but most of the time `mmap` is used instead, and the extra size
just slows down allocation of lexer states.

src/asm/lexer.cpp

@@ -11,6 +11,7 @@
 #include <inttypes.h>
 #include <limits.h>
 #include <math.h>
+#include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <unordered_map>