[lld] Check errors from expanding response files

Previously the response file expansion code would print the error, but
lld would not exit, which was odd.

lld does response file expansion in the different drivers, but it's also
done in main() first, so it's enough to check there.

By checking for these errors we would have caught when D136090
introduced a bug that made lld print errors for response files which
contained "-rpath @foo".

Differental revision: https://reviews.llvm.org/D137477