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.cc b/compiler/utils/x86/assembler_x86.cc
index 2203646..84cdb7d 100644
--- a/compiler/utils/x86/assembler_x86.cc
+++ b/compiler/utils/x86/assembler_x86.cc
@@ -1030,6 +1030,14 @@
 }
 
 
+void X86Assembler::cmpb(const Address& address, const Immediate& imm) {
+  AssemblerBuffer::EnsureCapacity ensured(&buffer_);
+  EmitUint8(0x80);
+  EmitOperand(7, address);
+  EmitUint8(imm.value() & 0xFF);
+}
+
+
 void X86Assembler::cmpw(const Address& address, const Immediate& imm) {
   AssemblerBuffer::EnsureCapacity ensured(&buffer_);
   EmitUint8(0x66);