fxt: fixing static linking for simgrid (suggested by Florent Pruvost)

configure.ac

@@ -1617,7 +1617,7 @@ if test x$use_fxt = xyes; then
 	if test x$enable_simgrid = xyes -a x$enable_shared = xno ; then
                 # simgrid's SMPI needs fxt to be linked in statically for
                 # variable privatization to work
-		FXT_LIBS="$(pkg-config --variable=libdir fxt)/libfxt.a -lrt"
+		FXT_LIBS="$(pkg-config --libs --static fxt)"
 	fi
 
         AC_ARG_ENABLE(paje-codelet-details, [AS_HELP_STRING([--enable-paje-codelet-details],