Check for dlopen() in the system libraries before trying -ldl.

Fixes compilation on BSDs.


git-svn-id: http://svn.xiph.org/trunk/ao@1367 0101bb08-14d6-0310-b084-bc0e0c8e3800

ao.m4

+# ao.m4
 # Configure paths for libao
 # Jack Moffitt <jack@icecast.org> 10-21-2000
 # Shamelessly stolen from Owen Taylor and Manish Singh
@@ -18,7 +19,15 @@ AC_ARG_ENABLE(aotest, [  --disable-aotest       Do not try to compile and run a
     AO_LIBS="-L$ao_prefix/lib"
   fi
 
-  AO_LIBS="$AO_LIBS -lao -ldl"
+  # see where dl* and friends live
+  AC_CHECK_FUNCS(dlopen, [AO_DL_LIBS=""], [
+    AC_CHECK_LIB(dl, dlopen, [AO_DL_LIBS="-ldl"], [
+      AC_MSG_ERROR([could not find dlopen() needed by libao sound drivers
+      your system may not be supported.])
+    ])
+  ])
+
+  AO_LIBS="$AO_LIBS -lao $AO_DL_LIBS"
 
   AC_MSG_CHECKING(for ao)
   no_ao=""