[PATCH] Fix internal error on unterminated --start-lib option.

[Cary Coutant]

> While I have you, can I ask how the gold maintainers run the test suite?
> Running x86_64, I noticed that several tests are broken on master. The
> incremental linking ones look like legitimate failures.

I've not yet upgraded to GCC 7; the test suite runs fine with GCC 6.

A few incremental test failures with GCC 7 have been reported (PR
21090, 22378, and 22309). I've been focused on PR 21090, which keeps
getting deeper [1], and I'm hoping that the other two are related to
that (but haven't yet tried to verify).

[1] Compiling with -fpie creates GOT entries, even when linking
without -pie, and --incremental-update fails to relocate the GOT
entries.

-cary