CMake: Improve checking for external libraries

Do not abort when libLZMA or libSecret can not be found, just show a warning.
Do not search for libSecret on macOS.
Disable libraries internally (not in cache) when not searching for them.

build/cmake/init.cmake

@@ -151,14 +151,18 @@ if(wxUSE_THREADS)
 endif()
 
 if(wxUSE_LIBLZMA)
-    find_package(LibLZMA REQUIRED)
+    find_package(LibLZMA)
+    if(NOT LIBLZMA_FOUND)
+        message(WARNING "libLZMA not found, LZMA compression won't be available")
+        wx_option_force_value(wxUSE_LIBLZMA OFF)
+    endif()
 endif()
 
 if(UNIX)
-    if(wxUSE_SECRETSTORE)
+    if(wxUSE_SECRETSTORE AND NOT APPLE)
         # The required APIs are always available under MSW and OS X but we must
         # have GNOME libsecret under Unix to be able to compile this class.
-        find_package(Libsecret REQUIRED)
+        find_package(Libsecret)
         if(NOT LIBSECRET_FOUND)
             message(WARNING "libsecret not found, wxSecretStore won't be available")
             wx_option_force_value(wxUSE_SECRETSTORE OFF)
@@ -293,9 +297,12 @@ if(wxUSE_GUI)
             message(WARNING "GStreamer not found, wxMediaCtrl won't be available")
             wx_option_force_value(wxUSE_MEDIACTRL OFF)
         endif()
+    else()
+        set(wxUSE_GSTREAMER OFF)
+        set(wxUSE_GSTREAMER_PLAYER OFF)
     endif()
 
-    if(UNIX AND wxUSE_LIBSDL)
+    if(wxUSE_SOUND AND UNIX AND wxUSE_LIBSDL)
         find_package(SDL2)
         if(NOT SDL2_FOUND)
             find_package(SDL)
@@ -304,6 +311,8 @@ if(wxUSE_GUI)
             message(WARNING "SDL not found, SDL Audio back-end won't be available")
             wx_option_force_value(wxUSE_LIBSDL OFF)
         endif()
+    else()
+        set(wxUSE_LIBSDL OFF)
     endif()
 
     if(wxUSE_NOTIFICATION_MESSAGE AND UNIX AND WXGTK2 AND wxUSE_LIBNOTIFY)
@@ -314,6 +323,8 @@ if(wxUSE_GUI)
         elseif((LIBNOTIFY_VERSION GREATER 0.7) OR (LIBNOTIFY_VERSION EQUAL 0.7))
             set(wxUSE_LIBNOTIFY_0_7 ON)
         endif()
+    else()
+        set(wxUSE_LIBNOTIFY OFF)
     endif()
 
     if(wxUSE_UIACTIONSIMULATOR AND UNIX AND WXGTK)
@@ -346,6 +357,8 @@ if(wxUSE_GUI)
             message(STATUS "libmspack not found")
             wx_option_force_value(wxUSE_LIBMSPACK OFF)
         endif()
+    else()
+        set(wxUSE_LIBMSPACK OFF)
     endif()
 
     if(WXGTK2 AND wxUSE_MIMETYPE AND wxUSE_LIBGNOMEVFS)
@@ -357,5 +370,7 @@ if(wxUSE_GUI)
             message(STATUS "libgnomevfs not found, library won't be used to associate MIME type")
             wx_option_force_value(wxUSE_LIBGNOMEVFS OFF)
         endif()
+    else()
+        set(wxUSE_LIBGNOMEVFS OFF)
     endif()
 endif()