Link against the system LibAtrac9 instead of fetching and building a private copy.

--- a/cmake/dependencies/atrac9.cmake
+++ b/cmake/dependencies/atrac9.cmake
@@ -1,27 +1,15 @@
 if(NOT WIN32 AND USE_ATRAC9)
-	FetchDependency(ATRAC9
-		DIR LibAtrac9
-		GIT_REPOSITORY https://github.com/Thealexbarney/LibAtrac9
-		GIT_TAG 6a9e00f6c7abd74d037fd210b6670d3cdb313049
-		GIT_UNSHALLOW ON
-	)
+	find_library(ATRAC9_LINK_PATH NAMES atrac9)
 	
-	if(ATRAC9_PATH)
-		set(ATRAC9_LINK_PATH ${ATRAC9_BIN}/bin/libatrac9.a)
+	if(ATRAC9_LINK_PATH)
+		set(ATRAC9_SOURCE "(system)")
 		
-		add_custom_target(ATRAC9_MAKE
-			COMMAND make static CFLAGS="-fPIC" OBJDIR="${ATRAC9_BIN}/obj" BINDIR="${ATRAC9_BIN}/bin" CC="${CMAKE_C_COMPILER}" AR="${CMAKE_AR}"
-			WORKING_DIRECTORY ${ATRAC9_PATH}/C
-			BYPRODUCTS ${ATRAC9_LINK_PATH} ${ATRAC9_BIN}
-		)
-		
-		add_library(atrac9 STATIC IMPORTED)
-		if(NOT EXISTS ${ATRAC9_LINK_PATH})
-			add_dependencies(atrac9 ATRAC9_MAKE)
-		endif()
+		add_library(atrac9 SHARED IMPORTED)
 		set_target_properties(atrac9 PROPERTIES
 			IMPORTED_LOCATION ${ATRAC9_LINK_PATH}
 		)
+	else()
+		set(USE_ATRAC9 OFF)
 	endif()
 endif()
 if(NOT USE_ATRAC9)