X87: [turbofan] Turn Math.clz32 into an inlinable builtin.

src/x87/lithium-codegen-x87.cc

Index: src/x87/lithium-codegen-x87.cc
diff --git a/src/x87/lithium-codegen-x87.cc b/src/x87/lithium-codegen-x87.cc
index 5a44e6e734e4c688678e6c76e77a06b0b13f0283..85a68f40538bfd668c0918aeb8c5eb9de7592639 100644
--- a/src/x87/lithium-codegen-x87.cc
+++ b/src/x87/lithium-codegen-x87.cc
@@ -4294,14 +4294,8 @@ void LCodeGen::DoMathLog(LMathLog* instr) {
 void LCodeGen::DoMathClz32(LMathClz32* instr) {
   Register input = ToRegister(instr->value());
   Register result = ToRegister(instr->result());
-  Label not_zero_input;
-  __ bsr(result, input);
 
-  __ j(not_zero, &not_zero_input);
-  __ Move(result, Immediate(63));  // 63^31 == 32
-
-  __ bind(&not_zero_input);
-  __ xor_(result, Immediate(31));  // for x in [0..31], 31^x == 31-x.
+  __ Lzcnt(result, input);
 }