Add cmpb instruction to x86 and x86_64 assembler

Change-Id: I43f41ef2fdf6475238f0987842aefb1c2eb6a36d
Signed-off-by: Serguei Katkov <serguei.i.katkov@intel.com>
diff --git a/compiler/utils/x86/assembler_x86_test.cc b/compiler/utils/x86/assembler_x86_test.cc
index 1d1df6e..28043c9 100644
--- a/compiler/utils/x86/assembler_x86_test.cc
+++ b/compiler/utils/x86/assembler_x86_test.cc
@@ -389,4 +389,10 @@
   DriverStr(expected, "near_label");
 }
 
+TEST_F(AssemblerX86Test, Cmpb) {
+  GetAssembler()->cmpb(x86::Address(x86::EDI, 128), x86::Immediate(0));
+  const char* expected = "cmpb $0, 128(%EDI)\n";
+  DriverStr(expected, "cmpb");
+}
+
 }  // namespace art