[clang] Workaround for MSVC ARM64 build performance regression (PR #65215)

[Alexander Smarus via cfe-commits]

lxbndr wrote:

A short summary of changes:
- added link to the issue
- narrowed checks to aim cl.exe only (clang-cl.exe doesn't need this)
- changed approach a bit. Now we're looking for /O2 and /O1 flags in the general flag set for the current configuration. Last effective found flag is suppressed and replaced with "same-minus-/Og" equivalent for corresponding O variant (either size or speed).

I believe this is the most careful way to adjust the build options and avoid conflicts with user flags. Basically, if you have /O_n_, you will get same optimizations except problematic one.

cc @tru @omjavaid 


https://github.com/llvm/llvm-project/pull/65215