GCC fails to bootstrap when configured with --enable-languages=all on
machines that have older versions of GNAT installed as the system Ada
compiler.  In configure, it's not sufficient to check whether gnat is
available, but whether a sufficiently recent version of GNAT is
installed.  This patch tweaks config/acx.m4 so that conftest.adb also
contains a reference to System.CRTL.int64 as required by the current
version of gcc/ada/osint.adb.  This fixes the build when the system
Ada is GNAT v4.8.5 (on Redhat 7) by disabling ada, but continues to
work fine when the system Ada is GNAT v11.3.1.

Tested in x86_64-pc-linux-gnu.  Ok for mainline?


2022-07-30  Roger Sayle  <roger@nextmovesoftware.com>

ChangeLog
        * config/acx.me (AC_PROG_GNAT): Update conftest.adb to include
        features required of the host gnat compiler.
        * configure: Regenerate.

Thanks in advance,
Roger
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