Remove non-address bits for longjmp resume breakpoint

Remove non-address bits for longjmp resume breakpoint

On 32-bit S390 targets the longjmp target address "naturally" has the
most significant bit set.  That bit indicates the addressing mode and
is not part of the address itself.  Thus, in analogy with similar
cases (like when computing the caller PC in
insert_step_resume_breakpoint_at_caller), this change removes
non-address bits from the longjmp target address before using it as a
breakpoint address.

Note that there are two ways for determining the longjmp target
address: via a probe or via a gdbarch method.  This change only
affects the probe method, because it is assumed that the address
returned by the gdbarch method is usable as-is.

This change was tested together with a patch that enables longjmp
probes in glibc for S/390:

  https://sourceware.org/ml/libc-alpha/2014-10/msg00277.html

gdb/ChangeLog:

	* gdb/infrun.c (process_event_stop_test): Apply
	gdbarch_addr_bits_remove to longjmp resume address.