cmake: convert luacheck test to custom target

Basically it is not actually a test and to make it align with
running luatest and luacov I converted it to a custom target too.

Author: ligurio

CMakeLists.txt

@@ -16,9 +16,8 @@ include_directories(${TARANTOOL_INCLUDE_DIRS})
 enable_testing()
 
 find_package(LuaCheck)
-add_test(
-  NAME luacheck
-  COMMAND ${LUACHECK} .
+add_custom_target(luacheck
+  COMMAND ${LUACHECK} ${PROJECT_SOURCE_DIR}
   WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}
 )