[Ada] Minimal binder

[Ada] Minimal binder

The new minimal binder option ("-minimal") suppresses the generation of
binder objects that are not strictly required for program operation.
This option is suitable for space constrained applications and comes
with the restriction that programs can no longer be debugged using GDB.

2019-07-11  Patrick Bernardi  <bernardi@adacore.com>

gcc/ada/

	* bindgen.adb (Gen_Main): Do not generate a reference to
	Ada_Main_Program_Name when the Minimal_Binder flag is set.
	(Gen_Output_File_Ada): Do not output GNAT_Version and
	Ada_Main_Program_Name info if Minimal_Binder flag is set.
	* bindusg.adb: Add documentation for new -minimal switch.
	* gnatbind.adb (Scan_Bind_Arg): Scan -minimal switch.
	* opt.ads: Add new global flag Minimal_Binder to indicate if the
	binder should not produce global variables.
	* doc/gnat_ugn/building_executable_programs_with_gnat.rst:
	Update documentation with new binder -minimal switch.
	* gnat_ugn.texi: Regenerate.

From-SVN: r273401