Seems this happened because the order of automake variables for modules
is not consistent.
module_tunnel_sink_la_LIBADD = $(MODULE_LIBADD) $(X11_LIBS)
module_tunnel_source_la_SOURCES = modules/module-tunnel.c
-module_tunnel_source_la_LDFLAGS = $(MODULE_LDFLAGS) $(X11_CFLAGS)
+module_tunnel_source_la_LDFLAGS = $(MODULE_LDFLAGS)
module_tunnel_source_la_LIBADD = $(MODULE_LIBADD) $(X11_LIBS)
-module_tunnel_source_la_CFLAGS = $(AM_CFLAGS) -DPA_MODULE_NAME=module_tunnel_source
+module_tunnel_source_la_CFLAGS = $(AM_CFLAGS) $(X11_CFLAGS) -DPA_MODULE_NAME=module_tunnel_source
module_loopback_la_SOURCES = modules/module-loopback.c
module_loopback_la_LDFLAGS = $(MODULE_LDFLAGS)