unittests: Force execution of $(UNITTEST_LIBS) build target
native: fix coding style
native: set optional path with unix socket option

fixes #1045
Merge pull request #1214 from LudwigOrtmann/issue-1045

native: unix socket path enhancement
Merge pull request #1238 from authmillenon/makefile-unittests

unittests: Force execution of $(UNITTEST_LIBS) build target