[cleanup][codegen] Fix -Wshadow warnings (attempt 2)

The fix in https://crrev.com/c/3283620 doesn't work, it was meant to be
a general way to fix shadow whenever ASM_CODE_COMMENT is used, by
appending the current line, via __LINE__ macro to the variable name.
However, __LINE__ is not expended correctly when it is directly part of
a variable name.

To fix the shadowing, we use UNIQUE_IDENTIFIER to give unique names.

Bug: v8:12244,v8:12245
Change-Id: I7b9b9da74d62023ac631ff0876f41e80971e2f09
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3291804
Auto-Submit: Zhi An Ng <zhin@chromium.org>
Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/main@{#78058}

src/codegen/assembler.h

@@ -39,6 +39,7 @@
 #include <memory>
 #include <unordered_map>
 
+#include "src/base/macros.h"
 #include "src/base/memory.h"
 #include "src/codegen/code-comments.h"
 #include "src/codegen/cpu-features.h"
@@ -470,7 +471,7 @@ class V8_EXPORT_PRIVATE V8_NODISCARD CpuFeatureScope {
 #ifdef V8_CODE_COMMENTS
 #define ASM_CODE_COMMENT(asm) ASM_CODE_COMMENT_STRING(asm, __func__)
 #define ASM_CODE_COMMENT_STRING(asm, comment) \
-  AssemblerBase::CodeComment asm_code_comment##__LINE__(asm, comment)
+  AssemblerBase::CodeComment UNIQUE_IDENTIFIER(asm_code_comment)(asm, comment)
 #else
 #define ASM_CODE_COMMENT(asm)
 #define ASM_CODE_COMMENT_STRING(asm, ...)