Port faster callbacks invocation to x64.

src/x64/assembler-x64.cc

Index: src/x64/assembler-x64.cc
diff --git a/src/x64/assembler-x64.cc b/src/x64/assembler-x64.cc
index c66666a73ae8cc828497b1df8da4d99ec0d9f838..d898b6659a40121d9f490639434a064bdc9fe9b6 100644
--- a/src/x64/assembler-x64.cc
+++ b/src/x64/assembler-x64.cc
@@ -1496,12 +1496,8 @@ void Assembler::movq(Register dst, int64_t value, RelocInfo::Mode rmode) {
 
 
 void Assembler::movq(Register dst, ExternalReference ref) {
-  EnsureSpace ensure_space(this);
-  last_pc_ = pc_;
-  emit_rex_64(dst);
-  emit(0xB8 | dst.low_bits());
-  emitq(reinterpret_cast<uintptr_t>(ref.address()),
-        RelocInfo::EXTERNAL_REFERENCE);
+  int64_t value = reinterpret_cast<int64_t>(ref.address());
+  movq(dst, value, RelocInfo::EXTERNAL_REFERENCE);
 }