Fix build failure caused by underlinking.

Gentoo-bug: 369697

--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -57,6 +57,8 @@
     #IF(ALSA_FOUND)
         ADD_DEFINITIONS(-D__LINUX_ALSASEQ__)
         LINK_LIBRARIES (asound)
+        LINK_LIBRARIES (GL)
+        LINK_LIBRARIES (pthread)
     #ELSE(ALSA_FOUND)
     #    MESSAGE(FATAL_ERROR "Please install the 'libasound2-dev' package and then try again")
     #ENDIF(ALSA_FOUND)