[PATCH] libstdc++: Use AS_IF in configure.ac

[Hans-Peter Nilsson]

> Date: Tue, 6 Jun 2023 16:30:12 +0100
> From: Jonathan Wakely via Gcc-patches <gcc-patches@gcc.gnu.org>

> On Thu, 1 Jun 2023 at 16:59, Jonathan Wakely via Libstdc++ <
> libstdc++@gcc.gnu.org> wrote:
> 
> > Tested x86_64-linux. I'd appreciate a second set of eyeballs on this
> > before I push it.
> >
> 
> Pushed to trunk now.

...as r14-1581-g97a5e8a2a48d16, after which (apparently)
*all* linking libstdc++ tests for cris-elf (a "newlib
target") get (for example):

FAIL: 17_intro/freestanding.cc (test for excess errors)
Excess errors:
/x/cris-elf/pre/cris-elf/bin/ld: cannot find -liconv: No such file or directory

(deduced from libstdc++.log and the commits in the range
ce2188e4320c..585c660f041c where 4144 regressions in
libstdc++ were introduced for cris-elf)

>From the generated configure and a brief RTFM for AS_IF, it
looks almost like AS_IF was "miscompiled" and behaving
literally AS_IF (!) in that the condition TEST1 (here
[$GLIBCXX_IS_NATIVE] seems to be emitted *after* the
RUN-IF-TRUE1 clause (the next 31 lines).  Not obvious what
went wrong.  I even tried regenerating configure.  HTH.

brgds, H-P