Adjust gdb.base/bp-permanent.exp for Cygwin

On Cygwin, all inferiors are multi-threaded, because both Windows and
the Cygwin runtime spawn a few helper threads.  Adjust the
gdb.base/bp-permanent.exp testcase to work with either single- or
multi-threaded inferiors.

Approved-by: Kevin Buettner <kevinb@redhat.com>
Change-Id: I28935b34fc9f739c2a5490e83aa4995d29927be2
1 file changed