gdb/testsuite: restore configure script

gdb/testsuite: restore configure script

Commit f99d1d37496f ("Remove gdb/testsuite/configure") removed
gdb/testsuite/configure, as anything gdb/testsuite/configure did could
be done by gdb/configure.

There is however one use case that popped up when this changed
propagated to downstream consumers, to run the testsuite on an already
built GDB.  In the workflow of ROCm-GDB at AMD, a GDB package is built
in a CI job.  This GDB package is then tested on different machines /
hardware configurations as part of other CI jobs.  To achieve this,
those CI jobs only configure the testsuite directory and run "make
check" with an appropriate board file.

In light of this use case, the way I see it is that gdb/testsuite could
be considered its own project.  It could be stored in a completely
different repo if we want to, it just happens to be stored inside gdb/.

Since the only downside of having gdb/testsuite/configure is that it
takes a few more seconds to run, but on the other hand it's quite useful
for some people, I propose re-adding it.

In a sense, this is revert of f99d1d37496f, but it's not a direct
git-revert, as some things have changed since.

gdb/ChangeLog:

	* configure.ac: Remove things that were moved from
	testsuite/configure.ac.
	* configure: Re-generate.

gdb/testsuite/ChangeLog:

	* configure.ac: Restore.
	* configure: Re-generate.
	* aclocal.m4: Re-generate.
	* Makefile.in (distclean): Add config.status.
	(Makefile): Adjust paths.
	(lib/pdtrace): Adjust paths.
	(config.status): Add.

Change-Id: Ic38c79485e1835712d9c99649c9dfb59667254f1