cet.m4 (GCC_CET_FLAGS): Default to --disable-cet, replace --enable-cet=default with --enable-cet=auto.

	* config/cet.m4 (GCC_CET_FLAGS): Default to --disable-cet, replace
	--enable-cet=default with --enable-cet=auto.

	* doc/install.texi: Document --disable-cet being the default and
	--enable-cet=auto.

	* configure: Regenerated.

From-SVN: r259487