Update check_elf_file.py for clang-r353983

This commit updates how `check_elf_file.py` parses the symbol name
because the `llvm-readobj` (from clang-r353983) does not print "@" if
the symbol is not versioned.

See also. https://reviews.llvm.org/D56319

Bug: 128959554
Test: CHECK_ELF_FILES=true make check-elf-files
Change-Id: I0dee5e505225e57750a2c86cf0d25a151c218eb1