refactor zstd cmake and prefer system lib

external/CMakeLists.txt

@@ -28,29 +28,7 @@ if (NOT TARGET nlohmann_json::nlohmann_json)
 	FetchContent_MakeAvailable(json)
 endif()
 
-if (NOT TARGET zstd::zstd)
-	# TODO: try find_package() first
-	# TODO: try pkg-config next (will work on most distros)
-
-	set(ZSTD_BUILD_STATIC ON)
-	set(ZSTD_BUILD_SHARED OFF)
-	set(ZSTD_BUILD_PROGRAMS OFF)
-	set(ZSTD_BUILD_CONTRIB OFF)
-	set(ZSTD_BUILD_TESTS OFF)
-	FetchContent_Declare(zstd
-		URL "https://github.com/facebook/zstd/releases/download/v1.5.6/zstd-1.5.6.tar.gz"
-		DOWNLOAD_EXTRACT_TIMESTAMP TRUE
-		SOURCE_SUBDIR build/cmake
-		EXCLUDE_FROM_ALL
-	)
-	FetchContent_MakeAvailable(zstd)
-
-	add_library(zstd INTERFACE) # somehow zstd fkd this up
-	target_include_directories(zstd INTERFACE ${zstd_SOURCE_DIR}/lib/)
-	target_link_libraries(zstd INTERFACE libzstd_static)
-	#TODO: new zstd also provides zstd::libzstd
-	add_library(zstd::zstd ALIAS zstd)
-endif()
+add_subdirectory(./zstd)
 
 #if (NOT TARGET solanaceae_plugin)
 	#FetchContent_Declare(solanaceae_plugin