[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/optimizing/code_generator_x86_64.h b/compiler/optimizing/code_generator_x86_64.h
index 3b3915f..41bebac 100644
--- a/compiler/optimizing/code_generator_x86_64.h
+++ b/compiler/optimizing/code_generator_x86_64.h
@@ -322,6 +322,9 @@
   // Load a 64 bit value into a register in the most efficient manner.
   void Load64BitValue(CpuRegister dest, int64_t value);
 
+  // Store a 64 bit value into a DoubleStackSlot in the most efficient manner.
+  void Store64BitValueToStack(Location dest, int64_t value);
+
  private:
   // Labels for each block that will be compiled.
   GrowableArray<Label> block_labels_;