[llvm][ELF] Add statistics on various section sizes (#102363)
Useful with other infrastructure that consume LLVM statistics to get an
idea of distribution of section sizes.
The breakdown of various section types is subject to change, this is
just an initial go at gather some sort of stats.
Example stats compiling X86ISelLowering.cpp (-g1):
```
"elf-object-writer.AllocROBytes": 308268,
"elf-object-writer.AllocRWBytes": 6240,
"elf-object-writer.AllocTextBytes": 1659203,
"elf-object-writer.DebugBytes": 3180386,
"elf-object-writer.OtherBytes": 5862,
"elf-object-writer.RelocationBytes": 2623440,
"elf-object-writer.StrtabBytes": 228599,
"elf-object-writer.SymtabBytes": 120336,
"elf-object-writer.UnwindBytes": 85216,
```
llvm-project
1baa6f75 - [llvm][ELF] Add statistics on various section sizes (#102363)
