It is not recommended to define type alias in C++ header file. cctest defines
type alias `using Label=CodeAssemblerLabel` in anonymous namespace under
namespace `v8::internal::compiler` in test-code-assembler.cc. This is fine
because this type alias is expected to take effect only in this .cc file. But in
jumbo build, multiple source files are combined as a single one, and the
previous `Label` type alias could shadow definition of `Label` from other header
file (for example, v8/src/codegen/label.h which is included by another .cc file)
This is totally unexpected and triggers bad class layout and accessing in the
latter .cc file for the places where `Label` is referenced.

This change fixes cctest from Windows ARM64 jumbo build, but it applies to
other architectures too.

Bug: chromium:893460
Change-Id: Ib2e9df76f6e3371b3940649668c5d13e6b36f028
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1788537Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Tom Tan <Tom.Tan@microsoft.com>
Cr-Commit-Position: refs/heads/master@{#63605}