re PR bootstrap/70704 (AIX bootstrap comparison failure)

	PR bootstrap/70704
	* configure.ac (--enable-stage1-checking): For --disable-checking or
	implicit --enable-checking, make sure extra flag matches in between
	stage1 and later checking.
	* configure: Regenerated.
gcc/
	* configure.ac (--enable-checking): Document extra flag, for
	non-release builds default to --enable-checking=yes,extra.
	If misc checking and extra checking, define CHECKING_P to 2 instead
	of 1.
	* common.opt (fchecking=): Add.
	* doc/invoke.texi (-fchecking=): Document.
	* doc/install.texi: Document --enable-checking changes.
	* configure: Regenerated.
	* config.in: Regenerated.
gcc/cp/
	* pt.c (build_non_dependent_expr): Use flag_checking > 1 instead of
	just flag_checking.

From-SVN: r235430