Revert -Wl, change to Makefile.osf, as the allegedly more standard

syntax apparently does not work for all toolchains on that platform.
Per Honda Shigehiro.

src/makefiles/Makefile.osf

 AROPT = crs
 DLSUFFIX = .so
 CFLAGS_SL =
-rpath = -Wl,-rpath -Wl,$(rpathdir)
+rpath = -rpath $(rpathdir)
 
 %.so: %.o
 	$(LD) -shared -expect_unresolved '*' -o $@ $<