[gdb/testsuite] Add PR gdb/26967 KFAIL in two more test-cases

On aarch64-linux (debian 12), when running test-case
gdb.base/longjmp-until-in-main.exp, I run into:
...
(gdb) until 33^M
warning: Breakpoint address adjusted from 0x70f727c678928489 to 0xfff727c678928489.^M
Warning:^M
Cannot insert breakpoint 0.^M
Cannot access memory at address 0xfff727c678928489^M
^M
0x0000fffff7e3a580 in siglongjmp () from /lib/aarch64-linux-gnu/libc.so.6^M
(gdb) FAIL: gdb.base/longjmp-until-in-main.exp: until $line, in main
...

This is PR gdb/26967: no longjmp probe is available:
...
(gdb) info probes stap libc ^longjmp$^M
No probes matched.^M
...
and glibc applies pointer mangling which makes it fairly difficult for gdb to
get the longjmp target.

There's a KFAIL for this in test-case gdb.base/longjmp.exp, added in commit
b5e7cd5c ("[gdb/testsuite] Add KFAILs in gdb.base/longjmp.exp").

Factor out new proc have_longjmp_probe, and use it to add similar KFAIL in
this and one more test-case.

Tested on aarch64-linux.

Approved-By: Tom Tromey <tom@tromey.com>