Since we no longer need to distribute s-stratt__xdr.adb, some code in
Makefile.rtl is now dead. Update the GNAT UG accordingly.
Tested on x86_64-pc-linux-gnu, committed on trunk
gcc/ada/
* Makefile.rtl: Remove dead code.
* doc/gnat_ugn/building_executable_programs_with_gnat.rst:
Currently we provide a separate implementation of Stream_Attributes via
s-stratt__xdr.adb which needs to be recompiled manually.
This change introduces instead a new binder switch to choose at bind
time which stream implementation to use and replaces s-stratt__xdr.adb
by a new unit System.Stream_A
