[Ada] Ignore exceptions in task termination handlers

[Ada] Ignore exceptions in task termination handlers

This patch fixes a bug in which if the environment task has a specific
termination handler, and that handler raises an exception, the handler
is called recursively, causing infinite recursion. The RM requires such
exceptions to be ignored.

gcc/ada/

	* libgnarl/s-solita.adb (Task_Termination_Handler_T): Ignore all
	exceptions propagated by Specific_Handler.
	* libgnarl/s-tassta.adb, libgnarl/s-taskin.ads: Minor.