Add ALSA include directories to fix compile on some systems.

CMakeLists.txt

@@ -54,6 +54,7 @@ elseif (UNIX AND NOT APPLE)
         if (NOT ALSA_FOUND)
             message(FATAL_ERROR "ALSA API requested but no ALSA dev libraries found")
         endif()
+        include_directories(${ALSA_INCLUDE_DIR})
         list(APPEND LINKLIBS ${ALSA_LIBRARY} ${CMAKE_THREAD_LIBS_INIT})
         add_definitions(-D__LINUX_ALSA__)
         message(STATUS "Using Linux ALSA")