[LLD][ELF] - Add a test case for code in Archive::fetch(). NFCI.
[LLD][ELF] - Add a test case for code in Archive::fetch(). NFCI.

This covers the following piece with a test.
https://github.com/llvm-mirror/lld/blob/master/ELF/InputFiles.cpp#L830

Thanks to Peter Collingbourne for providing the reproducer sample!

git-svn-id: f6089bf0e6284f307027cef4f64114ee9ebb0424@339114 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/lld,llvm-mirror/lld