[lld] Keep full library path in DT_NEEDED.

Fixes PR32572.

When
    (a) a library has no soname
and (b) library is given on the command line with path (and not through -L/-l flags)
DT_NEEDED entry for such library keeps the path as given.

This behavior is consistent with gold and bfd, and is used in compiler-rt test suite.

This is a second attempt after r300007 got reverted. This time relro-omagic test is
changed in a way to avoid hardcoding the path to the test directory in the objdump'd
binary.

llvm-svn: 300011