added -lpthread to jack.pc so that builds of clients will find pthreads even if they don't use it themselves

git-svn-id: svn+ssh://jackaudio.org/trunk/jack@1004 0c269be4-1314-0410-8aa9-9f06e86f4224

jack.pc.in

@@ -6,5 +6,5 @@ includedir=@includedir@
 Name: jack
 Description: the Jack Audio Connection Kit: a low-latency synchronous callback-based media server
 Version: @JACK_VERSION@
-Libs: -L${libdir} -ljack "@OS_LDFLAGS@"
+Libs: -L${libdir} -ljack -lpthread "@OS_LDFLAGS@"
 Cflags: -I${includedir}