Adding x86 compiler utils instructions and tests

Instructions added are (repne scasb), (repne movb),
and (repne cmpsb) for x86.
Instructions added is (repne scasb) for x86_64.

Test: m -j31 test-art-host-gtest-assembler_x86_test
      m -j31 test-art-host-gtest-assembler_x86_64_test

Change-Id: I137bf5fe1174b1dcc0166f7f2e0cffadbc0ca7f5
diff --git a/compiler/utils/x86_64/assembler_x86_64.h b/compiler/utils/x86_64/assembler_x86_64.h
index 3a4bfca..fdd3aa9 100644
--- a/compiler/utils/x86_64/assembler_x86_64.h
+++ b/compiler/utils/x86_64/assembler_x86_64.h
@@ -670,6 +670,7 @@
   void rolq(CpuRegister reg, const Immediate& imm);
   void rolq(CpuRegister operand, CpuRegister shifter);
 
+  void repne_scasb();
   void repne_scasw();
   void repe_cmpsw();
   void repe_cmpsl();