Revert "makefile fixup for sendmmsg-compat"

This reverts commit 950f98b703ca39c0c9756cd6f5b9fff17cf004d5.

Issue #25
Revert "Provide compatibility wrappers for {recv,send}mmsg"

This reverts commit c428803bc31400d01bf25ee3ef52b34e01121bbf.

Issue #25
Require both linkage *and* declarations for sendmmsg support

Issue #25
remove _UNQUOTED from a few AC_DEFINE where not needed