[ELF] Allow colons in the path.

This patch should fix the test when it runs on Windows, by allowing drive
letter separator (colon) in the path. Now all LLD ELF tests passed on MSVC
2012 32-bit. Hooray!

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@193978 91177308-0d34-0410-b5e6-96231b3b80d8