ada: Document gnatbind -Q switch

Add documentation for the -Q gnatbind switch in GNAT User's Guide and
improve gnatbind's help output for the switch to emphasize that it adds the
requested number of stacks to the secondary stack pool generated by the
binder.

gcc/ada/

	* bindusg.adb (Display): Make it clear -Q adds to the number of
	secondary stacks generated by the binder.
	* doc/gnat_ugn/building_executable_programs_with_gnat.rst:
	Document the -Q gnatbind switch and fix references to old
	runtimes.
	* gnat-style.texi: Regenerate.
	* gnat_rm.texi: Regenerate.
	* gnat_ugn.texi: Regenerate.

• [DBH] gcc/ada/bindusg.adb
• [DBH] gcc/ada/doc/gnat_ugn/building_executable_programs_with_gnat.rst
• [DBH] gcc/ada/gnat-style.texi
• [DBH] gcc/ada/gnat_rm.texi
• [DBH] gcc/ada/gnat_ugn.texi

ada: Generate runtime restrictions list when the standard library is suppressed

With the introduction of Jorvik support into the light-tasking runtime comes
the requirement to detect voliations of runtime restrictions (for example
Max_Entry_Queue_Length) where previously they could be hard coded in the
runtime. This means we now need the binder to populate
System.System.Restrictions.Run_Time_Restrictions when the standard library
is suppressed.

gcc/ada/

	* bindgen.adb (Gen_Adainit): Generate restrictions when standard
	library is suppressed.
	(Gen_Output_File_Ada): Ditto.
	(Gen_Restrictions): Ditto.

• [DBH] gcc/ada/bindgen.adb

ada: Do not perform local-exception-to-goto optimization on barrier functions

The local-exception-to-goto optimization is no longer applied to entry
barrier functions as entry barriers cannot contain exception handlers and
this optimization interferes with another optimization that occurs for
simple barrier functions.

In particular, the simple barrier optimization removes the push error label
statements generated by the local-exception-to-goto optimization. This
causes a Storage_Error in GIGI when the restriction No_Exception_Propagation
is  active and a protected object contains more than one simple entry
barrier.

gcc/ada/

	* exp_ch6.adb (Expand_N_Subprogram_Body): Do not perform
	local-exception-to- goto optimization on barrier functions.
	* exp_ch9.adb (Expand_Entry_Barrier): Simplify the if statement
	around the simple barrier optimization and remove an old, no
	longer relevant comment.

• [DBH] gcc/ada/exp_ch6.adb
• [DBH] gcc/ada/exp_ch9.adb