Cosmetic change: s/THRLIBS/THREADLIBS/

Use a more intuitive variable name.

plugins/Makefile.am

@@ -71,7 +71,7 @@ check_apt_LDADD = $(BASEOBJS)
 check_cluster_LDADD = $(BASEOBJS)
 check_dbi_LDADD = $(NETLIBS) $(DBILIBS)
 check_dig_LDADD = $(NETLIBS) $(MATHLIBS)
-check_disk_LDADD = $(BASEOBJS) $(THRLIBS)
+check_disk_LDADD = $(BASEOBJS) $(THREADLIBS)
 check_dns_LDADD = $(NETLIBS)
 check_dummy_LDADD = $(BASEOBJS)
 check_fping_LDADD = $(NETLIBS)