Porting Math.pow changes to x64.

src/x64/assembler-x64.h

Index: src/x64/assembler-x64.h
diff --git a/src/x64/assembler-x64.h b/src/x64/assembler-x64.h
index 1501d230b9fa4fbf3db949027129ffe833f10314..745850d822e68a003a338f689b5755c5545fb252 100644
--- a/src/x64/assembler-x64.h
+++ b/src/x64/assembler-x64.h
@@ -1277,6 +1277,9 @@ class Assembler : public AssemblerBase {
   void fcos();
   void fptan();
   void fyl2x();
+  void f2xm1();
+  void fscale();
+  void fninit();
 
   void frndint();