[optimizing] More x86_64 code improvements

Use the constant area some more, use 32-bit immediates in movq
instructions when possible, and other small tweaks.

Remove the commented out code for Math.Abs(float/double) as it would
fail for baseline compiler due to the output being the same as the
input.

Change-Id: Ifa39f1865b94cec2e1c0a99af3066a645e9d3618
Signed-off-by: Mark Mendell <mark.p.mendell@intel.com>
diff --git a/compiler/utils/x86_64/assembler_x86_64.h b/compiler/utils/x86_64/assembler_x86_64.h
index b8e5fb6..beca037 100644
--- a/compiler/utils/x86_64/assembler_x86_64.h
+++ b/compiler/utils/x86_64/assembler_x86_64.h
@@ -332,7 +332,7 @@
   void movq(CpuRegister dst, const Address& src);
   void movl(CpuRegister dst, const Address& src);
   void movq(const Address& dst, CpuRegister src);
-  void movq(const Address& dst, const Immediate& src);
+  void movq(const Address& dst, const Immediate& imm);
   void movl(const Address& dst, CpuRegister src);
   void movl(const Address& dst, const Immediate& imm);