cmake: let test-tool run the unit tests, too

The `test-tool` recently learned to run the unit tests. To this end, it
needs to link with `test-lib.c`, which was done in the `Makefile`, and
this patch does it in the CMake definition, too.

This is a companion of 44400f5 (t0080: turn t-basic unit test into
a helper, 2024-02-02).

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: dscho

contrib/buildsystems/CMakeLists.txt

@@ -1005,10 +1005,11 @@ endforeach()
 
 #test-tool
 parse_makefile_for_sources(test-tool_SOURCES "TEST_BUILTINS_OBJS")
+add_library(test-lib OBJECT ${CMAKE_SOURCE_DIR}/t/unit-tests/test-lib.c)
 
 list(TRANSFORM test-tool_SOURCES PREPEND "${CMAKE_SOURCE_DIR}/t/helper/")
 add_executable(test-tool ${CMAKE_SOURCE_DIR}/t/helper/test-tool.c ${test-tool_SOURCES} ${test-reftable_SOURCES})
-target_link_libraries(test-tool common-main)
+target_link_libraries(test-tool test-lib common-main)
 
 set_target_properties(test-fake-ssh test-tool
 			PROPERTIES RUNTIME_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/t/helper)