Handle libossaudio as an optional OSS library

CMakeLists.txt

@@ -904,6 +904,9 @@ IF(OSS_FOUND)
         SET(HAVE_OSS 1)
         SET(BACKENDS  "${BACKENDS} OSS,")
         SET(ALC_OBJS  ${ALC_OBJS} Alc/backends/oss.c)
+        IF(OSS_LIBRARIES)
+            ADD_BACKEND_LIBS(${OSS_LIBRARIES})
+        ENDIF()
     ENDIF()
 ENDIF()
 IF(ALSOFT_REQUIRE_OSS AND NOT HAVE_OSS)

cmake/FindOSS.cmake

@@ -2,8 +2,10 @@
 #
 #   OSS_FOUND        - True if OSS_INCLUDE_DIR is found
 #   OSS_INCLUDE_DIRS - Set when OSS_INCLUDE_DIR is found
+#   OSS_LIBRARIES    - Set when OSS_LIBRARY is found
 #
 #   OSS_INCLUDE_DIR - where to find sys/soundcard.h, etc.
+#   OSS_LIBRARY     - where to find libossaudio (optional).
 #
 
 find_path(OSS_INCLUDE_DIR
@@ -11,11 +13,21 @@ find_path(OSS_INCLUDE_DIR
           DOC "The OSS include directory"
 )
 
+find_library(OSS_LIBRARY
+             NAMES ossaudio
+             DOC "Optional OSS library"
+)
+
 include(FindPackageHandleStandardArgs)
 find_package_handle_standard_args(OSS  REQUIRED_VARS OSS_INCLUDE_DIR)
 
 if(OSS_FOUND)
     set(OSS_INCLUDE_DIRS ${OSS_INCLUDE_DIR})
+    if(OSS_LIBRARY)
+        set(OSS_LIBRARIES ${OSS_LIBRARY})
+    else()
+        unset(OSS_LIBRARIES)
+    endif()
 endif()
 
-mark_as_advanced(OSS_INCLUDE_DIR)
+mark_as_advanced(OSS_INCLUDE_DIR OSS_LIBRARY)