gdb/testsuite: Improve detection of bug gdb/24541

gdb/testsuite: Improve detection of bug gdb/24541

In bug gdb/24686 a testsuite failure was reported, this failure was
actually just another instance of bug gdb/24541, however, due to the
non-deterministic nature of bug gdb/24541 the testsuite pattern that
was intended to catch this bug failed.

This commit adds a second pattern to help detect gdb/24541, which
should change the FAIL reported in gdb/24686 into a KFAIL.

gdb/testsuite/ChangeLog:

	PR gdb/24686
	* gdb.mi/mi-catch-cpp-exceptions.exp: Add an extra pattern to
	improve detection of bug gdb/24541.