+In hints/os390.sh, selecting -Dusedl will default to *also* select
+-Duseshrplib. Having a shared plib not only requires LIBPATH to be set to
+the correct location of libperl.so but also makes it close to impossible
+to run more than one different perl that was built this way at the same
+time.
+
+All objects that are involved in -Dusedl builds should be compiled for
+this, probably by adding to all ccflags
+
+ -qexportall -qxplink -qdll -Wc,XPLINK,dll,EXPORTALL -Wl,XPLINK,dll
+
+=head3 Optimizing