gold: ensure file_counts_lock is initialized before using

gold: ensure file_counts_lock is initialized before using

Since upgrading to binutils 2.35 I've been experiencing random memory
corruption related crashes with ld.gold --threads. It's caused by
multiple threads concurrently pushing elements onto the shared
std::vector in File_read::record_file_read(). This vector is supposed to
be protected by file_counts_lock, but that is initialized lazily and
might be NULL when File_read::open() is called, in which case
Hold_optional_lock silently skips locking it.

Fix by calling the initialize() method before attempting to acquire the
lock, the same as other places that use file_counts_lock.

	PR 26827
	* fileread.cc (File_read::open): Ensure file_counts_lock is
	initialized.
	* testsuite/Makefile.am (check_PROGRAMS): Add a test that passes
	-Wl,--threads.
	* testsuite/Makefile.in: Regenerate.