Move generated math methods from platform to codegen

src/platform.h

Index: src/platform.h
diff --git a/src/platform.h b/src/platform.h
index 31b7bdfd36d2c270265ed095f9e5374a0a0685b8..764bd5408f38532a9880ca8d3020034e99941018 100644
--- a/src/platform.h
+++ b/src/platform.h
@@ -73,16 +73,6 @@ inline int lrint(double flt) {
 namespace v8 {
 namespace internal {
 
-double modulo(double x, double y);
-
-// Custom implementation of math functions.
-double fast_exp(double input);
-double fast_sqrt(double input);
-// The custom exp implementation needs 16KB of lookup data; initialize it
-// on demand.
-void lazily_initialize_fast_exp();
-
-
 // ----------------------------------------------------------------------------
 // Fast TLS support