patch-CMakeLists.txt

--- CMakeLists.txt.orig	2023-09-08 23:16:28 UTC
+++ CMakeLists.txt
@@ -8,7 +8,9 @@ include(CMakeDependentOption)
 set(CMAKE_MODULE_PATH ${CMAKE_MODULE_PATH} "${CMAKE_SOURCE_DIR}/cmake/Modules/")
 
 include(CMakeDependentOption)
-include(cmake/CPM.cmake)
+if (SRB2_CONFIG_SYSTEM_LIBRARIES)
+	include(cmake/CPM.cmake)
+endif()
 
 file(STRINGS src/version.h SRB2_VERSION)
 string(REGEX MATCH "[0-9]+\\.[0-9.]+" SRB2_VERSION ${SRB2_VERSION})
@@ -79,7 +81,8 @@ set(SRB2_CONFIG_ASSET_DIRECTORY "" CACHE PATH "Path to
 # SRB2_CONFIG_PROFILEMODE is probably superceded by some CMake setting.
 option(SRB2_CONFIG_PROFILEMODE "Compile for profiling (GCC only)." OFF)
 set(SRB2_CONFIG_ASSET_DIRECTORY "" CACHE PATH "Path to directory that contains all asset files for the installer. If set, assets will be part of installation and cpack.")
-
+ 
+if (NOT SRB2_CONFIG_SYSTEM_LIBRARIES)
 if(SRB2_CONFIG_ENABLE_TESTS)
 	# https://github.com/catchorg/Catch2
 	CPMAddPackage(
@@ -98,6 +101,7 @@ endif()
 	target_compile_features(srb2tests PRIVATE c_std_11 cxx_std_17)
 	catch_discover_tests(srb2tests)
 endif()
+endif()
 
 # Enable CCache
 # (Set USE_CCACHE=ON to use, CCACHE_OPTIONS for options)
@@ -114,11 +118,13 @@ else()
 		endif()
 	endif()
 else()
+	if (NOT SRB2_CONFIG_SYSTEM_LIBRARIES)
 	CPMAddPackage(
 		NAME Ccache.cmake
 		GITHUB_REPOSITORY TheLartians/Ccache.cmake
 		VERSION 1.2
 	)
+endif()
 endif()
 
 # Dependencies