Tweak gdbserver_tests/mcinfcallWSRU.stderrB.exp to match more gdb versions.

Some gdb versions don't show the source line:number after switching
threads in #0  0x........ in do_burn (). Filter "at line:number" out
and don't expect it.

git-svn-id: svn://svn.valgrind.org/valgrind/trunk@14427 a5019735-40e9-0310-863c-91ae7b9d1cf9
--> 3.10.0.BETA1


git-svn-id: svn://svn.valgrind.org/valgrind/trunk@14428 a5019735-40e9-0310-863c-91ae7b9d1cf9