This patch makes the configure adds -D_CALL_ELF=1 when compiler does
not define _CALL_ELF (versions before powerpc64le support). It cleans
up compiler warnings on old compiler where _CALL_ELF is not defined
on powerpc64(be) builds.
It does by add a new config.make variable for configure-deduced
CPPFLAGS and accumulate into that (confix-extra-cppflags). It also
generalizes libc_extra_cflags so it accumulates in sysdeps configure
fragmenets.
Autoconf is tested for and run if needed only when --enable-maintainer-mode
is used on configure. This results in the autom4te.cache directory only
being written in the source directory during configure if automatic
autoconf usage is requested.
Fixes BZ #14120.
Autoconf has been deprecating configure.in for quite a long time.
Rename all our configure.in and preconfigure.in files to .ac.
Signed-off-by: Mike Frysinger <vapier@gentoo.org>