libfabric: remove a few warnings

Embedding libfabric is a temporary measure; I'm removing some warning
notifications so that the output isn't so cluttered (we're getting
the real warnings fixed upstream, but the OMPI community doesn't
really care/need to see the warnings in the meantime).

opal/mca/common/libfabric/configure.m4

@@ -194,6 +194,8 @@ AC_DEFUN([_OPAL_COMMON_LIBFABRIC_SETUP_LIBFABRIC_EMBEDDED],[
             for flag in $CFLAGS; do
                 case $flag in
                 -pedantic) ;;
+                -Wmissing-prototypes) ;;
+                -Wsign-compare) ;;
                 *) opal_common_libfabric_embedded_CFLAGS="$opal_common_libfabric_embedded_CFLAGS $flag" ;;
                 esac
             done