[CodeGen] -fsanitize=alignment: add cl::opt sanitize-alignment-builtin to...

[CodeGen] -fsanitize=alignment: add cl::opt sanitize-alignment-builtin to disable memcpy instrumentation (#69240)

Deploying #67766 to a large internal codebase uncovers many bugs (many
are
probably benign but need cleaning up). There are also issues in
high-profile
open-source projects like v8. Add a cl::opt to disable builtin
instrumentation
for -fsanitize=alignment to help large codebase users.

In the long term, this cl::opt option may still be useful to debug
-fsanitize=alignment instrumentation on builtins, so we probably want to
keep it around.