If I comment out the caller of identifyELFSectionStartAndEndSymbols, check-llvm will still pass.
The encapsulation symbol supported by ELF linkers is __start_<sectionname>, not __start...
Also, linker created __start_<sectionname> symbols have protected visibility so that the executable and shared objects can have multiple definitions.

I think this area may be worth improving, but I'll need to learn more about JIT first...