tweak of Math.abs in its x64 stub

src/ia32/stub-cache-ia32.cc

Index: src/ia32/stub-cache-ia32.cc
===================================================================
--- src/ia32/stub-cache-ia32.cc	(revision 16112)
+++ src/ia32/stub-cache-ia32.cc	(working copy)
@@ -2479,6 +2479,8 @@
   STATIC_ASSERT(kSmiTag == 0);
   __ JumpIfNotSmi(eax, &not_smi);
 
+  // Branchless abs implementation, refer to below:
+  // http://graphics.stanford.edu/~seander/bithacks.html#IntegerAbs
   // Set ebx to 1...1 (== -1) if the argument is negative, or to 0...0
   // otherwise.
   __ mov(ebx, eax);