dep: zmqpp: don't specify namespace while inside same namespace
dep: zmqpp: don't define htonll and ntohll if already #defined

is the case with osx: defined in /usr/include/sys/_endian.h
dep: zmqpp: add diff for htonll/ntohll workaround
Merge pull request #13431 from bloerwald/fix_zmqpp_htonll_and_ntohll_on_osx

dep: zmqpp: fix: don't define htonll and ntohll if already #defined