[compiler-rt] [compiler-rt] Use mangled function names on ARM64EC (PR #137960)

[Saleem Abdulrasool via llvm-commits]

https://github.com/compnerd commented:

I wonder if there is a way to unify `SYMBOL_IS_FUNC` and `FUNC_SYMBOL`. We have a number of different places where we indicate that a label is a function, and it seems it would be very confusing for most to know which one belongs where.

https://github.com/llvm/llvm-project/pull/137960