vcl: better handlig of ldp apis that rely on gnu source

vcl: better handlig of ldp apis that rely on gnu source

Control use of apis that rely on _GNU_SOURCE being defined with compile
time macro.

Also fixes sendmmsg and recvmmsg which were not probably wrapped.

Type: improvement

Signed-off-by: Florin Coras <[email protected]>
Change-Id: I207de23210d4b9dc960bb4289159502760c5614d
(cherry picked from commit 3684794336602435b91b91a1dc5bd9401a974432)