[gdb/testsuite] Fix gdb.base/reset-catchpoint-cond.exp with --with-expat=no

When building gdb with --with-expat=no and running test-case
gdb.base/reset-catchpoint-cond.exp we get:
...
(gdb) catch syscall write^M
warning: Can not parse XML syscalls information; \
  XML support was disabled at compile time.^M
Unknown syscall name 'write'.^M
(gdb) FAIL: $exp: mode=syscall: catch syscall write
...

Fix this by skipping the test for --with-expat=no.

Tested on x86_64-linux.