Shared libruby also needs MAINLIBS for jemalloc

configure.ac

@@ -3869,6 +3869,7 @@ AS_IF([test -n "${LIBS}"], [
     MAINFLAGS=`echo " $MAINLIBS " | sed "s|$libspat"'||;s/^ *//;s/ *$//'`
 ])
 LIBRUBYARG_STATIC="${LIBRUBYARG_STATIC} \$(MAINLIBS)"
+LIBRUBYARG_SHARED="${LIBRUBYARG_SHARED} \$(MAINLIBS)"
 CPPFLAGS="$CPPFLAGS "'$(DEFS)'
 test -z "$CPPFLAGS" || CPPFLAGS="$CPPFLAGS "; CPPFLAGS="$CPPFLAGS"'${cppflags}'
 AS_IF([test -n "${cflags+set}"], [