Implemented the Word64Clz TurboFan operator for x64, arm64, and mips64.

src/compiler/x64/instruction-codes-x64.h

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_COMPILER_X64_INSTRUCTION_CODES_X64_H_
 #define V8_COMPILER_X64_INSTRUCTION_CODES_X64_H_
 
 namespace v8 {
 namespace internal {
 namespace compiler {
@@ skipping 28 matching lines @@
   V(X64Neg)                        \
   V(X64Neg32)                      \
   V(X64Shl)                        \
   V(X64Shl32)                      \
   V(X64Shr)                        \
   V(X64Shr32)                      \
   V(X64Sar)                        \
   V(X64Sar32)                      \
   V(X64Ror)                        \
   V(X64Ror32)                      \
+  V(X64Lzcnt)                      \
   V(X64Lzcnt32)                    \
   V(X64Tzcnt32)                    \
   V(X64Popcnt32)                   \
   V(SSEFloat32Cmp)                 \
   V(SSEFloat32Add)                 \
   V(SSEFloat32Sub)                 \
   V(SSEFloat32Mul)                 \
   V(SSEFloat32Div)                 \
   V(SSEFloat32Abs)                 \
   V(SSEFloat32Neg)                 \
@@ skipping 97 matching lines @@
   V(M1I)  /* [      %r2*1 + K] */      \
   V(M2I)  /* [      %r2*2 + K] */      \
   V(M4I)  /* [      %r2*4 + K] */      \
   V(M8I)  /* [      %r2*8 + K] */
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_X64_INSTRUCTION_CODES_X64_H_