[Bug bootstrap/112534] [14 regression] build failure after r14-5424-gdb50aea6259545 using gcc 4.8.5

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112534

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
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                 CC|                            |jakub at gcc dot gnu.org

--- Comment #5 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
The problem is that the toplevel configure (which is autoconf 2.69 as pretty
much everything in gcc) uses the older AC_PROG_CC, which only checks for
-std=gnu99 -std=c99 -c99 -AC99 -D_STDC_C99= -qlanglvl=extc99, not for
-std=gnu11.
And sets
CC = @CC@
in toplevel Makefile.in to
CC = gcc -std=gnu99
in toplevel objdir Makefile.  That gets then passed to in-tree gettext (if
present, I really don't think you need it on powerpc64-linux-gnu, perhaps
download_prerequisities should be smarter and check if gettext is really
needed) configure (where it just means
CC is set there to gcc -std=gnu99 -std=gnu11 in gettext/Makefile), but worse is
passed as CC="gcc -std=gnu99" in environment down when doing make all in the
gettext subdir.
I think that is something very similar to how CXX="g++ -std=c++11" is being
passed down
to in-tree isl build and breaks with recent isl which wants to use C++17 or
what.
Strangely, in my x86_64-linux toplevel Makefile I only have
CC = gcc
CXX = g++ -std=c++11
Dunno why it hasn't added -std=gnu99 there, maybe because that gcc already
defaults to gnu17?  Anyway, even when CC = gcc, I think that is passed down to
make of the in-tree compilations.
So, I guess if we don't want to switch to autoconf 2.70 or later (which I think
is a lot of work), one possibility if we know gettext relies on C11 and newest
ISL relies on C++17 (does it really?) would be to add explicit probing in
configure for -std=gnu11 or -std=c11 and if that works, pass it down in the
gettext build case; and similarly for isl.  Maybe better not in CC/CXX but in
CFLAGS/CXXFLAGS?
The propagation of flags is done in $(HOST_EXPORTS) and for stage2+
$(POSTSTAGE1_HOST_EXPORTS).

Looking around in Makefile.def, I see e.g. for gmp/mpfr we use
                extra_make_flags='AM_CFLAGS="-DNO_ASM"';
and for isl
                extra_make_flags='V=1';
Dunno if it would work to add for the gettext case
                extra_make_flags='CFLAGS="$(CFLAGS) @C11_CFLAGS@"';
with configure check for C11_FLAGS or something similar.