Extended-remote exec test

Extended-remote exec test

This patch updates several exec-related tests and some of the library
functions in order to get them running with extended-remote.  There were
three changes that were required, as follows:

In gdb.base/foll-exec.exp, use 'clean_start' in place of proc 'zap_session'
to reset the state of the debugger between tests.  This sets 'remote
exec-file' to execute the correct binary file in each subsequent test.

In gdb.base/pie-execl.exp, there is an expect statement with an expression
that is used to match output from both gdb and the program under debug.
For the remote target, this had to be split into two expressions, using
$inferior_spawn_id to match the output from the program.

Because I had encountered problems with extended-remote exec events in
non-stop mode in my manual testing, I added non-stop testing to the
non-ldr-exc-[1234].exp tests.  In order to set non-stop mode for remote
targets, it is necessary to 'set non-stop on' after gdb has started, but
before it connects to gdbserver.  This is done using 'save_vars' to set
non-stop mode in GDBFLAGS, so GDB sets non-stop mode on startup.

gdb/testsuite/ChangeLog:

	* gdb.base/foll-exec.c: Add copyright header.  Fix
	formatting issues.
	* gdb.base/foll-exec.exp (zap_session): Delete proc.
	(do_exec_tests): Use clean_restart in place of zap_session,
	and for test initialization.  Fix formatting issues.  Use
	fail in place of perror.
	* gdb.base/pie-execl.exp (main): Use 'inferior_spawn_id' in
	an expect statement to match an expression with output from
	the program under debug.
	* gdb.threads/non-ldr-exc-1.exp (do_test, main): Add
	non-stop tests and pass stop mode argument to clean_restart.
	Use save_vars to enable non-stop in GDBFLAGS.
	* gdb.threads/non-ldr-exc-2.exp: Likewise.
	* gdb.threads/non-ldr-exc-3.exp: Likewise.
	* gdb.threads/non-ldr-exc-4.exp: Likewise.