Configuration question

[Steve Ellcey <sje at hpsje dot cup dot hp dot com>]

I have run into a libstdc++ configuration issue and was wondering if it
is a known issue or not.

My build failed because the compiler I am using to build GCC and
libstdc++ does not have wchar support and does not define mbstate_t.
The compiler (and library) that I am creating however, do support wchar
and do define mbstate_t.  Both compilers are GCC, the old one does not
include a -D that the new one does.  mbstate_t (defined in the system
header files) is only seen when this define is set.

The problem is that the libstdc++ configure script is using the original
GCC to check for the existence of mbstate_t (doesn't find it) and using
that information to say that it needs to define mbstate_t when compiling
libstdc++, but libstdc++ is compiled with the newly built GCC which
does have an mbstate_t from the system header files.  Shouldn't the
libstdc++ configure script use the new GCC when checking things with
AC_TRY_COMPILE.  Or is this just not possible?  Is this why some tests
don't use AC_TRY_COMPILE but say "Fake what AC_TRY_COMPILE does"?  See
acinclude.m4 for these comments, there is no explanation about why it is
faking what AC_TRY_COMPILE does.

Steve Ellcey
sje@cup.hp.com