[llvm-profgen] Switch to DWARF-based symbol and ranges

It happened a bug that some callsite name in the profile is not a real function, it turned out that there're some non-function symbol from the ELF text section, e.g. the global accessible branch label and also recalled that we can have one function being split into multiple ranges. We shouldn't count samples for those are not the entry of the real function.

So this change tried to fix this issue by switching to use the name or ranges from DWARF-based debug info, the range of which assure it's the real function start. For the split functions, we assume that the real entry function's DWARF name should always match the symbol table name.

The switching is also consistent with the body samples' symbol which is from DWARF.

Reviewed By: hoy, wenlei

Differential Revision: https://reviews.llvm.org/D112282