configure: duplicate/incorrect order of -lrt

'-lrt' flag duplication/incorrect order
would cause 'undefined reference to clock_gettime' error during compilation time.

Before fix:
... -o qemu-bridge-helper qemu-bridge-helper.o    -lrt -pthread -lgthread-2.0 -lrt -lglib-2.0
After fix:
... -o qemu-bridge-helper qemu-bridge-helper.o    -pthread -lgthread-2.0 -lrt -lglib-2.0

Reference:
http://hi.baidu.com/sanitywolf/item/7a8b69c1e76dd220a0b50ab1Signed-off-by: NRick Liu <yrliu.ca@gmail.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

configure

@@ -3452,9 +3452,9 @@ EOF
 if compile_prog "" "" ; then
   :
 # we need pthread for static linking. use previous pthread test result
-elif compile_prog "" "-lrt $pthread_lib" ; then
-  LIBS="-lrt $LIBS"
-  libs_qga="-lrt $libs_qga"
+elif compile_prog "" "$pthread_lib -lrt" ; then
+  LIBS="$LIBS -lrt"
+  libs_qga="$libs_qga -lrt"
 fi
 
 if test "$darwin" != "yes" -a "$mingw32" != "yes" -a "$solaris" != yes -a \