Always organize test artifacts in a directory hierarchy

Always organize test artifacts in a directory hierarchy

When running tests in parallel, each test puts its generated files in a
different directory, under "outputs".  I think it would be nice if it
was always the case, as it would isolate the test cases a bit more.  An
artifact created by a test wouldn't get overwritten by another test.

Also, it makes it easier to clean up.  A lot of executables are left all
over the place because their names do not appear in gdb.*/Makefile.  If
everything is in "outputs", then we just have to delete that directory
(which we already do).

At the same time it makes the gdb.foo directories and their Makefiles
useless in the build directory, since they are pretty much only used for
cleaning.

What do you think?

gdb/testsuite/ChangeLog:

	* Makefile.in (ALL_SUBDIRS): Remove.
	(clean mostlyclean): Do not recurse in ALL_SUBDIRS.
	(distclean maintainer-clean realclean): Likewise.
	* configure.ac (AC_OUTPUT): Remove gdb.*/Makefile.
	* configure: Regenerate.
	* gdb.ada/Makefile.in: Delete.
	* gdb.arch/Makefile.in: Likewise.
	* gdb.asm/Makefile.in: Likewise.
	* gdb.base/Makefile.in: Likewise.
	* gdb.btrace/Makefile.in: Likewise.
	* gdb.cell/Makefile.in: Likewise.
	* gdb.compile/Makefile.in: Likewise.
	* gdb.cp/Makefile.in: Likewise.
	* gdb.disasm/Makefile.in: Likewise.
	* gdb.dlang/Makefile.in: Likewise.
	* gdb.dwarf2/Makefile.in: Likewise.
	* gdb.fortran/Makefile.in: Likewise.
	* gdb.gdb/Makefile.in: Likewise.
	* gdb.go/Makefile.in: Likewise.
	* gdb.guile/Makefile.in: Likewise.
	* gdb.java/Makefile.in: Likewise.
	* gdb.linespec/Makefile.in: Likewise.
	* gdb.mi/Makefile.in: Likewise.
	* gdb.modula2/Makefile.in: Likewise.
	* gdb.multi/Makefile.in: Likewise.
	* gdb.objc/Makefile.in: Likewise.
	* gdb.opencl/Makefile.in: Likewise.
	* gdb.opt/Makefile.in: Likewise.
	* gdb.pascal/Makefile.in: Likewise.
	* gdb.perf/Makefile.in: Likewise.
	* gdb.python/Makefile.in: Likewise.
	* gdb.reverse/Makefile.in: Likewise.
	* gdb.server/Makefile.in: Likewise.
	* gdb.stabs/Makefile.in: Likewise.
	* gdb.threads/Makefile.in: Likewise.
	* gdb.trace/Makefile.in: Likewise.
	* gdb.xml/Makefile.in: Likewise.
	* lib/gdb.exp (make_gdb_parallel_path): Add check for
	GDB_PARALLEL.
	(standard_output_file): Remove check for GDB_PARALLEL, always
	return path in outputs/$subdir/$testname.