Add basic support for compiling on RISC OS

CMakeLists.txt

@@ -129,7 +129,7 @@ elseif(CMAKE_SYSTEM_NAME MATCHES "Haiku.*")
 endif()
 
 # Don't mistake osx for unix
-if(UNIX AND NOT APPLE)
+if(UNIX AND NOT APPLE AND NOT RISCOS)
   set(UNIX_SYS ON)
 else()
   set(UNIX_SYS OFF)
@@ -341,7 +341,7 @@ set_option(VIDEO_OPENGLES      "Include OpenGL ES support" ON)
 set_option(PTHREADS            "Use POSIX threads for multi-threading" ${SDL_PTHREADS_ENABLED_BY_DEFAULT})
 dep_option(PTHREADS_SEM        "Use pthread semaphores" ON "PTHREADS" OFF)
 set_option(SDL_DLOPEN          "Use dlopen for shared object loading" ${SDL_DLOPEN_ENABLED_BY_DEFAULT})
-set_option(OSS                 "Support the OSS audio API" ${UNIX_SYS})
+dep_option(OSS                 "Support the OSS audio API" ON "UNIX_SYS OR RISCOS" OFF)
 set_option(ALSA                "Support the ALSA audio API" ${UNIX_SYS})
 dep_option(ALSA_SHARED         "Dynamically load ALSA audio support" ON "ALSA" OFF)
 set_option(JACK                "Support the JACK audio API" ${UNIX_SYS})
@@ -1091,7 +1091,7 @@ elseif(EMSCRIPTEN)
     endif()
   endif()
 
-elseif(UNIX AND NOT APPLE AND NOT ANDROID)
+elseif(UNIX AND NOT APPLE AND NOT ANDROID AND NOT RISCOS)
   if(SDL_AUDIO)
     if(SYSV5 OR SOLARIS OR HPUX)
         set(SDL_AUDIO_DRIVER_SUNAUDIO 1)
@@ -1814,6 +1814,24 @@ elseif(HAIKU)
   endif()
 
   CheckPTHREAD()
+
+elseif(RISCOS)
+  if(SDL_TIMERS)
+    set(SDL_TIMER_UNIX 1)
+    file(GLOB TIMER_SOURCES ${SDL2_SOURCE_DIR}/src/timer/unix/*.c)
+    set(SOURCE_FILES ${SOURCE_FILES} ${TIMER_SOURCES})
+    set(HAVE_SDL_TIMERS TRUE)
+
+    if(CLOCK_GETTIME)
+      set(HAVE_CLOCK_GETTIME 1)
+    endif()
+  endif()
+
+  CheckPTHREAD()
+
+  if(SDL_AUDIO)
+    CheckOSS()
+  endif()
 endif()
 
 if(VIDEO_VULKAN)