[binutils] Use "scasb %nacl:(%rdi),%al,%r15" pseudocommand, not series of commands

Review URL: http://codereview.chromium.org/2870084
diff --git a/gcc/config/i386/i386.md b/gcc/config/i386/i386.md
index a29f022..be9d784 100644
--- a/gcc/config/i386/i386.md
+++ b/gcc/config/i386/i386.md
@@ -20368,9 +20368,7 @@
 {
  if (TARGET_NACL)
   {
-    /* Note: %rdi is used, but in reality it's memory read, not store */
-    return "movl\t%%edi, %%edi\nleaq\t(%%r15,%%rdi), %%rdi\n"
-	   "repnz scasb"
+    return "repnz scasb %%nacl:(%%rdi),%%al,%%r15"
 	   "\nmovl\t%%edi, %%edi";
   }
  else