sha256_4way: do not include unnecessary headers, when !4way

Reported by lfm

sha256_4way.c

@@ -4,15 +4,16 @@
 
 // tcatm's 4-way 128-bit SSE2 SHA-256
 
+#include "miner.h"
+
+#ifdef WANT_SSE2_4WAY
+
 #include <string.h>
 #include <assert.h>
 
 #include <xmmintrin.h>
 #include <stdint.h>
 #include <stdio.h>
-#include "miner.h"
-
-#ifdef WANT_SSE2_4WAY
 
 #define NPAR 32