Merge branch 'ps/clar-unit-test'

Import clar unit tests framework libgit2 folks invented for our use. * ps/clar-unit-test: Makefile: rename clar-related variables to avoid confusion clar: add CMake support t/unit-tests: convert ctype tests to use clar t/unit-tests: convert strvec tests to use clar t/unit-tests: implement test driver Makefile: wire up the clar unit testing framework Makefile: do not use sparse on third-party sources Makefile: make hdr-check depend on generated headers Makefile: fix sparse dependency on GENERATED_H clar: stop including `shellapi.h` unnecessarily clar(win32): avoid compile error due to unused `fs_copy()` clar: avoid compile error with mingw-w64 t/clar: fix compatibility with NonStop t: import the clar unit testing framework t: do not pass GIT_TEST_OPTS to unit tests with prove