[Bug c/51730] New: [4.7 Regression] autoconf 2.60 through 2.67 stdbool.h check fails with GCC 4.7

["jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51730

             Bug #: 51730
           Summary: [4.7 Regression] autoconf 2.60 through 2.67 stdbool.h
                    check fails with GCC 4.7
    Classification: Unclassified
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: jakub@gcc.gnu.org
                CC: jsm28@gcc.gnu.org


During a distro mass rebuild, I found that many packages still have configure
generated with autoconf 2.60 through 2.67, and these autoconf contain a not
strictly valid C:
         /* Catch a bug in IBM AIX xlc compiler version 6.0.0.0
            reported by James Lemley on 2005-10-05; see
           
http://lists.gnu.org/archive/html/bug-coreutils/2005-10/msg00086.html
            This test is not quite right, since xlc is allowed to
            reject this program, as the initializer for xlcbug is
            not one of the forms that C requires support for.
            However, doing the test right would require a runtime
            test, and that would make cross-compilation harder.
            Let us hope that IBM fixes the xlc bug, and also adds
            support for this kind of constant expression.  In the
            meantime, this test will reject xlc, which is OK, since
            our stdbool.h substitute should suffice.  We also test
            this with GCC, where it should work, to detect more
            quickly whether someone messes up the test in the
            future.  */
         char digs[] = "0123456789";
         int xlcbug = 1 / (&(digs + 5)[-2 + (_Bool) 1] == &digs[4] ? 1 : -1);
check.  Until http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=172958
GCC has been accepting this though, and I suppose we don't want to fold array
refs that way when generating code.  Would it be possible to fold it that way
(try harder) just when we know we are not going to generate code based on it
(or when we know we'd error out otherwise)?  I know it sounds like an ugly
hack,
unfortunately autoconf 2.6[0-7] generated configure scripts are going to be
around for many years and the stdbool.h checks would fail in hundreds of
packages.