Fix creation of stamp-h by gdb's configure script

Fix creation of stamp-h by gdb's configure script

I happened to notice that "make" would always print:

    CONFIG_HEADERS=config.h:config.in \
      CONFIG_COMMANDS="default depdir" \
      CONFIG_FILES= \
      CONFIG_LINKS= \
      /bin/sh config.status
    config.status: creating config.h
    config.status: config.h is unchanged

on every rebuild.  This seems to have changed due to an autoconf
upgrade at some point in the past.  In the autoconf gdb uses now, it
works to use AC_CONFIG_HEADERS and then create the stamp file via the
"commands" argument.

This patch also fixes up Makefile.in to use the new-style
config.status invocation.  It's no longer necessary to pass the output
file names via environment variables.

gdb/ChangeLog
2019-10-17  Tom Tromey  <tromey@adacore.com>

	* configure: Rebuild.
	* configure.ac: Use AC_CONFIG_HEADERS.  Create stamp-h there, not
	in AC_CONFIG_FILES invocation.
	* Makefile.in (Makefile, data-directory/Makefile, stamp-h): Use
	new-style config.status invocation.

gdb/gdbserver/ChangeLog
2019-10-17  Tom Tromey  <tromey@adacore.com>

	* configure: Rebuild.
	* configure.ac: Use AC_CONFIG_HEADERS.  Create stamp-h there, not
	in AC_CONFIG_FILES invocation.
	* Makefile.in (stamp-h, Makefile): Use new-style config.status
	invocation.

Change-Id: Ia0530d1c5b9756812d29ddb8dc1062326155e61e