Add support for skipping individual MPIX tests

If --enable_strictmpi is passed to configure, we need to skip non-MPI-standard tests.
Here is how you can do that. Suppose you have an MPIX test foobar, you need

1) In Makefile.am, to skip building foobar, add

    if BUILD_MPIX_TESTS
    noinst_PROGRAMS += foobar
    endif

  Note: There is no tab indentions before noinst_PROGRAMS

2) In testlist.in (please convert testlist to testlist.in if necessary), to skip
   running foobar, add

    @mpix@ foobar 2
Signed-off-by: Pavan Balaji <balaji@anl.gov>

test/mpi/configure.ac

@@ -464,6 +464,18 @@ if test "$FROM_MPICH" = "yes" -a "$enable_strictmpi" = "no" ; then
 fi
 AC_SUBST(MPI_HAS_MPIX)
 
+# Prepend @mpix@ to lines of tests in testlist.in which are MPIX tests so that
+# we can skip running these tests when we do strict MPI test.
+mpix="#"
+if test "$enable_strictmpi" = "no"; then
+    mpix=""
+fi
+AC_SUBST(mpix)
+
+# Use the conditional variable BUILD_MPIX_TESTS to conditionally add MPIX tests
+# to noninst_PROGRAMS to skip building the tests when we do strict MPI test
+AM_CONDITIONAL([BUILD_MPIX_TESTS], [test "$enable_strictmpi" = "no"])
+
 # preserve these values across a reconfigure
 AC_ARG_VAR([WRAPPER_CFLAGS],[])
 AC_ARG_VAR([WRAPPER_CPPFLAGS],[])