[test] Don't start elf-dump until lld-core is done writing the output.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@176205 91177308-0d34-0410-b5e6-96231b3b80d8
[lld][ELF] Order segments

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@176207 91177308-0d34-0410-b5e6-96231b3b80d8