[Ada] Add a Is_Foreign_Exception predicate to GNAT.Exception_Actions

Useful to check if an occurrence caught by a "when others" choice originates
from a foreign language, e.g. C++.

2018-05-23  Olivier Hainque  <hainque@adacore.com>

gcc/ada/

	* libgnat/g-excact.ads (Is_Foreign_Exception): New predicate.
	* libgnat/g-excact.adb: Implement.

From-SVN: r260588

gcc/ada/ChangeLog

+2018-05-23  Olivier Hainque  <hainque@adacore.com>
+
+	* libgnat/g-excact.ads (Is_Foreign_Exception): New predicate.
+	* libgnat/g-excact.adb: Implement.
+
 2018-05-23  Ed Schonberg  <schonberg@adacore.com>
 
 	* sem_ch5.adb (Analyze_Iterator_Specification): If a subtype indication

gcc/ada/libgnat/g-excact.adb

@@ -91,6 +91,19 @@ package body GNAT.Exception_Actions is
 
    procedure Core_Dump (Occurrence : Exception_Occurrence) is separate;
 
+   --------------------------
+   -- Is_Foreign_Exception --
+   --------------------------
+
+   function Is_Foreign_Exception (E : Exception_Occurrence) return Boolean is
+      Foreign_Exception : aliased Exception_Data;
+      pragma Import
+        (Ada, Foreign_Exception, "system__exceptions__foreign_exception");
+   begin
+      return (To_Data (Exception_Identity (E))
+                = Foreign_Exception'Unchecked_Access);
+   end Is_Foreign_Exception;
+
    ----------------
    -- Name_To_Id --
    ----------------

gcc/ada/libgnat/g-excact.ads

@@ -29,9 +29,11 @@
 --                                                                          --
 ------------------------------------------------------------------------------
 
---  This package provides support for callbacks on exceptions
+--  This package provides support for callbacks on exceptions as well as
+--  exception-related utility subprograms of possible interest together with
+--  exception actions or more generally.
 
---  These callbacks are called immediately when either a specific exception,
+--  The callbacks are called immediately when either a specific exception,
 --  or any exception, is raised, before any other actions taken by raise, in
 --  particular before any unwinding of the stack occurs.
 
@@ -85,6 +87,10 @@ package GNAT.Exception_Actions is
    --  Note: All non-predefined exceptions will return Null_Id for programs
    --  compiled with pragma Restriction (No_Exception_Registration)
 
+   function Is_Foreign_Exception (E : Exception_Occurrence) return Boolean;
+   --  Tell whether the exception occurrence E represents a foreign exception,
+   --  such as one raised in C++ and caught by a when others choice in Ada.
+
    function Registered_Exceptions_Count return Natural;
    --  Return the number of exceptions that have been registered so far.
    --  Exceptions declared locally will not appear in this list until their