[builtins] Introduce proper Float64Log2 and Float64Log10 operators.

src/assembler.h

Index: src/assembler.h
diff --git a/src/assembler.h b/src/assembler.h
index c9f5b5904c7820019f1d4629be96fa4f42778364..38078f3d22c8cbf4327d8efe72b1446fadbd2185 100644
--- a/src/assembler.h
+++ b/src/assembler.h
@@ -1046,6 +1046,8 @@ class ExternalReference BASE_EMBEDDED {
   static ExternalReference ieee754_atan2_function(Isolate* isolate);
   static ExternalReference ieee754_log_function(Isolate* isolate);
   static ExternalReference ieee754_log1p_function(Isolate* isolate);
+  static ExternalReference ieee754_log2_function(Isolate* isolate);
+  static ExternalReference ieee754_log10_function(Isolate* isolate);
 
   static ExternalReference math_exp_constants(int constant_index);
   static ExternalReference math_exp_log_table();