Depend on protobuf using its cmake config

FindProtobuf provided by CMake forgets that it should depend on libabsl,
and link fails.

This change makes it to use files provided by Protobuf library, which
don't miss that important detail. That also required switch from
protobuf_generate_cpp() to protobuf_generate() because that's the
function which it has. FindProtobuf.cmake also provides
protobuf_generate() but only since CMake 3.13.

Fix #7272

CMakeLists.txt

@@ -45,7 +45,7 @@ endif(OPENGL_FOUND)
 find_package(Boost REQUIRED)
 find_package(Gettext REQUIRED)
 find_package(PkgConfig REQUIRED)
-find_package(Protobuf REQUIRED)
+find_package(protobuf REQUIRED)
 find_package(FFTW3)
 find_package(ALSA)
 if (NOT APPLE)

ext/libclementine-remote/CMakeLists.txt

@@ -6,14 +6,14 @@ set(MESSAGES
   remotecontrolmessages.proto
 )
 
-protobuf_generate_cpp(PROTO_SOURCES PROTO_HEADERS ${MESSAGES})
-
 add_library(libclementine-remote STATIC
-  ${PROTO_SOURCES}
+  ${MESSAGES}
 )
 
+protobuf_generate(TARGET libclementine-remote LANGUAGE cpp)
+
 target_link_libraries(libclementine-remote
-  ${PROTOBUF_LIBRARY}
   libclementine-common
+  protobuf::libprotobuf
 )
 

ext/libclementine-tagreader/CMakeLists.txt

@@ -28,16 +28,16 @@ optional_source(HAVE_GOOGLE_DRIVE
 
 qt5_wrap_cpp(MOC ${HEADERS})
 
-protobuf_generate_cpp(PROTO_SOURCES PROTO_HEADERS ${MESSAGES})
-
 add_library(libclementine-tagreader STATIC
-  ${PROTO_SOURCES}
+  ${MESSAGES}
   ${SOURCES}
   ${MOC}
 )
 
+protobuf_generate(TARGET libclementine-tagreader LANGUAGE cpp)
+
 target_link_libraries(libclementine-tagreader
-  ${PROTOBUF_LIBRARY}
   libclementine-common
+  protobuf::libprotobuf
 )