[gdb/testsuite] Handle pipe2 syscall in gdb.base/catch-syscall.exp

When running test-case gdb.reverse/pipe-reverse.exp on openSUSE Tumbleweed,
I run into:
...
(gdb) continue^M
Continuing.^M
^M
Catchpoint 2 (returned from syscall pipe2), in pipe () from /lib64/libc.so.6^M
(gdb) FAIL: gdb.base/catch-syscall.exp: without arguments: \
  syscall pipe has returned
...

The current glibc on Tumbleweed is 2.35, which contains commit
"linux: Implement pipe in terms of __NR_pipe2", and consequently syscall pipe2
is used instead of syscall pipe.

Fix this by detecting whether syscall pipe or pipe2 is used before running the
tests.

Tested on x86_64-linux, specifically on:
- openSUSE Tumbleweed (with glibc 2.35), and
- openSUSE Leap 15.3 (with glibc 2.31).

On openSUSE Tumbleweed + target board unix/-m32, this exposes:
...
(gdb) catch syscall pipe2^M
Unknown syscall name 'pipe2'.^M
...
which will be fixed in a folllow-up patch.

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=29056

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