Also check for strerror_r in gdbserver

Also check for strerror_r in gdbserver

I forgot to do this in b231e86ac9608056ea837e24d42a878927f5787a

Since safe_strerror is in gdbsupport, gdbserver also needs to
check for strerror_r, although it's less critical since gdbserver
does not use threads as much.

gdb/gdbserver/ChangeLog:

2019-10-31  Christian Biesinger  <cbiesinger@google.com>

	* config.in: Regenerate.
	* configure: Regenerate.
	* configure.ac: Also check for strerror_r.

Change-Id: I6a67c8543cd7a28d6dc94f5986f56abcb55727fe