libxlu: avoid linker warnings

Recent ld warns about libxenlight.so's dependency libraries not being
available, which can be easily avoided by not just passing the raw
library name on ld's command line.

In the course of checking how things fit together (I originally
suspected the warning to come from the linking of xl) I also noticed a
stray L in SHLIB_libxenguest, which gets removed at once.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/tools/Rules.mk
+++ b/tools/Rules.mk
@@ -40,7 +40,7 @@ SHLIB_libxenctrl  = -Wl,-rpath-link=$(XE
 
 CFLAGS_libxenguest = -I$(XEN_LIBXC)/include $(CFLAGS_xeninclude)
 LDLIBS_libxenguest = $(XEN_LIBXC)/libxenguest$(libextension)
-SHLIB_libxenguest  = -Wl,-rpath-link=L$(XEN_LIBXC)
+SHLIB_libxenguest  = -Wl,-rpath-link=$(XEN_LIBXC)
 
 CFLAGS_libxenstore = -I$(XEN_XENSTORE)/include $(CFLAGS_xeninclude)
 LDLIBS_libxenstore = $(XEN_XENSTORE)/libxenstore$(libextension)
--- a/tools/libxl/Makefile
+++ b/tools/libxl/Makefile
@@ -41,7 +41,7 @@ LDFLAGS += $(PTHREAD_LDFLAGS)
 LIBXL_LIBS += $(PTHREAD_LIBS)
 LIBXL_LIBS += $(LIBXL_LIBS-y)
 
-LIBXLU_LIBS = libxenlight.so
+LIBXLU_LIBS = $(LDLIBS_libxenlight)
 
 LIBXL_OBJS-y = osdeps.o libxl_paths.o libxl_bootloader.o flexarray.o
 ifeq ($(LIBXL_BLKTAP),y)