Revert basenames_may_differ patch

Revert basenames_may_differ patch

Commit a0c1ffedc regressed certain cases coming from Eclipse.
See PR breakpoints/24915.

This patch reverts the commit for the gdb 9 release.

gdb/ChangeLog
2020-02-07  Tom Tromey  <tromey@adacore.com>

	PR breakpoints/24915:
	* source.c (find_and_open_source): Do not check basenames_may_differ.

gdb/testsuite/ChangeLog
2020-02-07  Tom Tromey  <tromey@adacore.com>

	PR breakpoints/24915:
	* gdb.base/annotate-symlink.exp: Use setup_xfail.

Change-Id: Iadbf42f35eb40c95ad32b2108ae25d8f199998bd