[gdb/testsuite] Rewrite catch-follow-exec.exp

[gdb/testsuite] Rewrite catch-follow-exec.exp

There are two problems with the current catch-follow-exec.exp:
- INTERNAL_GDBFLAGS (containing the datadir setting) is not used
- remote host testing doesn't work

Fix the former by using gdb_spawn_with_cmdline_opts.  Fix the latter by
requiring gdb-native.

Build on x86_64-linux with and without ubsan, and tested.

2018-10-16  Tom de Vries  <tdevries@suse.de>

	PR gdb/23730
	* gdb.base/catch-follow-exec.c: Add copyright notice.
	* gdb.base/catch-follow-exec.exp: Rewrite to use
	gdb_spawn_with_cmdline_opts.  Require gdb-native.