[clang] [CallGraph] Collect callables from global variable initializers (PR #206458)

[Balázs Benics via cfe-commits]

steakhal wrote:

The unfortunate consequence of having stuff enabled by default in clang (eg. For analysis based diags. Such as fall through, no return, etc.) that this part is enabled by default.
This is also a great benefit, but prompts me asking: have you measured the implications of this on build times?

https://github.com/llvm/llvm-project/pull/206458