Use find_package Protobuf CONFIG

CMakeLists.txt

@@ -117,9 +117,14 @@ else()
   find_package(Iconv)
 endif()
 find_package(GnuTLS REQUIRED)
-find_package(Protobuf REQUIRED)
-if(NOT Protobuf_PROTOC_EXECUTABLE)
-  message(FATAL_ERROR "Missing protobuf compiler.")
+if(NOT APPLE)
+  find_package(Protobuf CONFIG)
+endif()
+if(NOT Protobuf_FOUND)
+  find_package(Protobuf REQUIRED)
+endif()
+if(NOT TARGET protobuf::protoc)
+  message(FATAL_ERROR "Missing Protobuf compiler.")
 endif()
 if(LINUX)
   find_package(ALSA REQUIRED)