Make headers-check an object library

This will skip linking step

src/openrct2/CMakeLists.txt

@@ -185,7 +185,7 @@ endif()
 # - GCC 8 does not support -Wno-pragma-once-outside-header
 # - Other compilers status unknown
 if ("${CMAKE_CXX_COMPILER_ID}" STREQUAL "Clang")
-    add_library(${PROJECT}-headers-check ${OPENRCT2_CORE_HEADERS})
+    add_library(${PROJECT}-headers-check OBJECT ${OPENRCT2_CORE_HEADERS})
     set_target_properties(${PROJECT}-headers-check PROPERTIES LINKER_LANGUAGE CXX)
     set_source_files_properties(${OPENRCT2_CORE_HEADERS} PROPERTIES LANGUAGE CXX)
     add_definitions("-x c++ -Wno-pragma-once-outside-header -Wno-unused-const-variable")