[LLD] [COFF] Restore the current dir as the first entry in the search path (#67857)

Before af744f0b, the first entry
among the search paths was the empty string, indicating searching
in (or starting from) the current directory. After
af744f0b, the toolchain/clang
specific lib directories were added at the head of the search path.

This would cause lookups of literal file names or relative paths
to match paths in the toolchain, if there are coincidental files
with similar names there, even if they would be find in the current
directory as well.

Change addClangLibSearchPaths to append to the list like all other
operations on searchPaths - but move the invocation of the
function to the right place in the sequence.

This fixes #67779.