libxl: Use PTHREAD_CFLAGS, LDFLAGS, LIBS

This is going to be needed for pthread_atfork.  It is a mystery why it
hasn't been needed before.

Signed-off-by: Ian Jackson <ian.jackson@eu.citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
Committed-by: Ian Jackson <Ian.Jackson@eu.citrix.com>

tools/libxl/Makefile

@@ -22,6 +22,10 @@ endif
 LIBXL_LIBS =
 LIBXL_LIBS = $(LDLIBS_libxenctrl) $(LDLIBS_libxenguest) $(LDLIBS_libxenstore) $(LDLIBS_libblktapctl) $(UTIL_LIBS) $(LIBUUID_LIBS)
 
+CFLAGS += $(PTHREAD_CFLAGS)
+LDFLAGS += $(PTHREAD_LDFLAGS)
+LIBXL_LIBS += $(PTHREAD_LIBS)
+
 LIBXLU_LIBS =
 
 LIBXL_OBJS-y = osdeps.o libxl_paths.o libxl_bootloader.o flexarray.o