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

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.