Be more careful than just exporting CPPFLAGS (or not) to sub-
configure scripts. This fixes a bug in which --enable-visibility
would cause PRRTE's configure to fail, because the top-level
configure added -Wmissing-prototypes to CPPFLAGS and then
the subconfigure added -Werror at one point. In general,
blindly exporting all the CPPFLAGS OMPI adds was a bad idea, so
we instead only export precious variables if they were
set in the calling environment, on the command line of the
top-level configure, or explicitly added to the sub-
configure environment (like CPPFLAGS for PMIx/PRRTE).
Add some envirnoment scrubbing/saving/restore wrappers and
modify PAC_CONFIG_SUBDIR_ARGS to play a little nicer with
precious variables so that this all works.
Signed-off-by: Brian Barrett <bbarrett@amazon.com>
