gh-130090: Support PGO for clang-cl

[chris-eibl]

Per encouragement from @Fidget-Spinner in faster-cpython/ideas#690 (comment) opened as a draft PR:

Support PGO for clang-cl on Windows using a similar approach as done in the Linux makefiles for clang.
I separate the clang-cl profiles into e.g. obj\314amd64_PGInstrument\__clang_profiles, so that they don't clash with different build configurations.

Since pythoncore is built first and not in parallel, this was the easiest spot for me.
Fore sure room for improvements, I am definitely far from being an msbuild / vcxproj expert :)

BTW, clang-cl PGO takes far less time to build compared to MSVC, because

• running the instrumented pgo tests is much faster
• the PGO step is faster

Some thoughts:

• Linux uses -flto-thin to improve build time over execution time. Tried it, doesn't cost much in run time, but speeds up the build a lot.
• There are still many warnings. I've fixed many of them, if interested, we can do them in follow-up PRs. IMHO, some of them are not benign, e.g.

..\PC\launcher2.c(1081,34): warning : result of comparison of constant 191 with expression of type 'char' is always false [-Wtautological-constant-out-of-range-compare] [e:\cpython_clang\PCbuild\pywlauncher.vcxproj]
..\PC\launcher2.c(1081,18): warning : result of comparison of constant 187 with expression of type 'char' is always false [-Wtautological-constant-out-of-range-compare] [e:\cpython_clang\PCbuild\pywlauncher.vcxproj]

• let clang-cl benefit from _Py_HOT_FUNCTION, etc. Most probably in follow up PRs (very simple and small)

• Issue: Support PGO for clang-cl #130090