configure.ac: Rewrite DGUX check to use GC_CFLAGS, and -O0 check to remove the need for MY_CFLAGS.

2010-10-28  Paolo Bonzini  <bonzini@gnu.org>

	* configure.ac: Rewrite DGUX check to use GC_CFLAGS, and -O0 check
	to remove the need for MY_CFLAGS.
	* Makefile.am: Do not use @...@ substitutions.  Use AM_CXXFLAGS,
	AM_CFLAGS and AM_LDFLAGS instead of redefining LTCOMPILE and LINK.
	Use "override" to disable -O2 when required.
	* configure: Regenerate.
	* Makefile.in: Regenerate.
	* include/Makefile.in: Regenerate.

From-SVN: r166028