Find OpenAL the proper way

CMakeModules/FindOpenAL.cmake

@@ -0,0 +1,59 @@
+#  Copyright Matus Chochlik.
+#  Distributed under the Boost Software License, Version 1.0.
+#  See accompanying file LICENSE_1_0.txt or copy at
+#   http://www.boost.org/LICENSE_1_0.txt
+#
+#  2016-05-30: Updated for FlightGear --EMH--
+#
+unset(OPENAL_INCLUDE_DIRS)
+set(OPENAL_FOUND 0)
+#
+# try to find AL/al.h
+find_path(
+	OPENAL_AL_H_DIR AL/al.h
+	PATHS ${HEADER_SEARCH_PATHS}
+	NO_DEFAULT_PATH
+)
+# if that didn't work try the system directories
+if((NOT OPENAL_AL_H_DIR) OR (NOT EXISTS ${OPENAL_AL_H_DIR}))
+	find_path(OPENAL_AL_H_DIR AL/al.h)
+endif()
+# if found append it to the include directories
+if((OPENAL_AL_H_DIR) AND (EXISTS ${OPENAL_AL_H_DIR}))
+	set(OPENAL_INCLUDE_DIRS ${OPENAL_INCLUDE_DIRS} ${OPENAL_AL_H_DIR})
+	set(HAVE_AL_H true)
+	set(OPENAL_FOUND 1)
+endif()
+#
+#
+# try to find AL/alext.h
+find_path(
+	OPENAL_ALEXT_H_DIR AL/alext.h
+	PATHS ${HEADER_SEARCH_PATHS}
+	NO_DEFAULT_PATH
+)
+# if that didn't work try the system directories
+if((NOT OPENAL_ALEXT_H_DIR) OR (NOT EXISTS ${OPENAL_ALEXT_H_DIR}))
+	find_path(OPENAL_ALEXT_H_DIR AL/alext.h)
+endif()
+#
+if((OPENAL_ALEXT_H_DIR) AND (EXISTS ${OPENAL_ALEXT_H_DIR}))
+	set(OPENAL_INCLUDE_DIRS ${OPENAL_INCLUDE_DIRS} ${OPENAL_ALEXT_H_DIR})
+	set(HAVE_ALEXT_H true)
+endif()
+
+# try to find the AL library
+find_library(
+	OPENAL_LIBRARY NAMES openal
+	PATHS ${LIBRARY_SEARCH_PATHS}
+	NO_DEFAULT_PATH
+)
+if(NOT OPENAL_LIBRARY)
+	find_library(OPENAL_LIBRARY NAMES openal)
+endif()
+
+set(OPENAL_LIBRARIES "")
+if(OPENAL_LIBRARY AND EXISTS ${OPENAL_LIBRARY})
+	set(OPENAL_LIBRARIES ${OPENAL_LIBRARIES} ${OPENAL_LIBRARY})
+endif()
+