b=22967 s/AC_LANG_CONFTEST/LB_LINUX_CONFTEST/

There was a macro update in more recent releases of autoconf that requires
us to use AC_LANG_CONFTEST instead of the LB_LINUX_CONFTEST that we currently
use.  The problem using LB_LINUX_CONFTEST causes is that as configure is
determining capabilities and setting capability flags, these are not being
used when compiling further conftest.c programs.

So for example if a macro determines if foo is available and then sets FOO
if it is, and then a test in a subsequent macro tries to use FOO, it will
find it undefined.

i=mjmac
i=adilger