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

Documentation/technical/unit-tests.txt

@@ -203,6 +203,7 @@ GitHub / GitLab stars to estimate this.
 :criterion: https://github.com/Snaipe/Criterion[Criterion]
 :c-tap: https://github.com/rra/c-tap-harness/[C TAP]
 :check: https://libcheck.github.io/check/[Check]
+:clar: https://github.com/clar-test/clar[Clar]
 
 [format="csv",options="header",width="33%",subs="specialcharacters,attributes,quotes,macros"]
 |=====
@@ -212,6 +213,7 @@ Framework,"<<license,License>>","<<vendorable-or-ubiquitous,Vendorable or ubiqui
 {criterion},{mit},{false},{partial},{true},{true},{true},{true},{true},{false},{true},19,1800
 {c-tap},{expat},{true},{partial},{partial},{true},{false},{true},{false},{false},{false},4,33
 {check},{lgpl},{false},{partial},{true},{true},{true},{false},{false},{false},{true},17,973
+{clar},{isc},{false},{partial},{true},{true},{true},{true},{false},{false},{true},1,192
 |=====
 
 === Additional framework candidates