[Ada] Remove unnecessary dead code after calls to nonreturning procedures

A new warning about unreachable code that follows calls to procedures
with No_Return would flag some dead defensive code. Comments next to
this code suggest that it was added to please some ancient version of
the compiler, but recent releases of GNAT do not require such a code.

gcc/ada/

	* gnatls.adb (Corresponding_Sdep_Entry): Remove dead return
	statement in defensive path; there is another return statement
	for a normal execution of this routine, so rule Ada RM 6.5(5),
	which requires function to have at least one return statement is
	still satisfied.
	(Gnatls): Remove dead, call to nonreturning Exit_Program after
	Output_License_Information which itself does not return.
	* libgnat/a-exstat.adb (Bad_EO): Remove raise statement that was
	meant to please some ancient version of GNAT.
	* libgnat/g-awk.adb (Raise_With_Info): Likewise.
	* sem_attr.adb (Check_Reference): Remove dead return statement;
	rule Ada RM 6.5(5), which requires function to have at least one
	return statement is still satisfied.
	(Analyze_Attribute): Remove dead exit statement.
	(Check_Reference): Same as above.
	* sem_ch12.adb (Instantiate_Formal_Package): Remove dead raise
	statement; it was inconsistent with other calls to
	Abandon_Instantiation, which are not followed by a raise
	statement.
	* sem_prag.adb (Process_Convention): Remove dead defensive
	assignment.
	(Interrupt_State): Remove dead defensive exit statement.
	(Do_SPARK_Mode): Likewise.
	* sfn_scan.adb (Scan_String): Remove dead defensive assignment.

gcc/ada/gnatls.adb

@@ -319,7 +319,6 @@ procedure Gnatls is
       Write_Eol;
       Error_Msg ("wrong ALI format, can't find dependency line for $ in {");
       Exit_Program (E_Fatal);
-      return No_Sdep_Id;
    end Corresponding_Sdep_Entry;
 
    -------------------------
@@ -2051,7 +2050,6 @@ begin
    if License then
       if Arg_Count = 2 then
          Output_License_Information;
-         Exit_Program (E_Success);
 
       else
          Set_Standard_Error;

gcc/ada/libgnat/a-exstat.adb

@@ -109,13 +109,6 @@ package body Stream_Attributes is
          Raise_Exception
            (Program_Error'Identity,
             "bad exception occurrence in stream input");
-
-         --  The following junk raise of Program_Error is required because
-         --  this is a No_Return procedure, and unfortunately Raise_Exception
-         --  can return (this particular call can't, but the back end is not
-         --  clever enough to know that).
-
-         raise Program_Error;
       end Bad_EO;
 
       procedure Next_String is

gcc/ada/libgnat/g-awk.adb

@@ -1211,7 +1211,6 @@ package body GNAT.AWK is
       Exceptions.Raise_Exception
         (E,
          '[' & Filename & ':' & Line & "] " & Message);
-      raise Constraint_Error; -- to please GNAT as this is a No_Return proc
    end Raise_With_Info;
 
    ---------------

gcc/ada/sem_attr.adb

@@ -4747,7 +4747,6 @@ package body Sem_Attr is
                   Error_Attr
                     ("prefix of attribute % cannot reference local entities",
                      Nod);
-                  return Abandon;
                else
                   return OK;
                end if;
@@ -4989,7 +4988,6 @@ package body Sem_Attr is
             else
                Error_Attr
                  ("attribute % cannot appear in body or accept statement", N);
-               exit;
             end if;
          end loop;
 
@@ -5383,7 +5381,6 @@ package body Sem_Attr is
                   Error_Attr
                     ("prefix of attribute % cannot reference local entities",
                      Nod);
-                  return Abandon;
 
                --  Otherwise keep inspecting the prefix
 

gcc/ada/sem_ch12.adb

@@ -10572,7 +10572,6 @@ package body Sem_Ch12 is
          Error_Msg_N
            ("expect package instance to instantiate formal", Actual);
          Abandon_Instantiation (Actual);
-         raise Program_Error;
 
       else
          Actual_Pack := Entity (Actual);

gcc/ada/sem_prag.adb

@@ -8336,7 +8336,6 @@ package body Sem_Prag is
                Error_Pragma_Arg
                  ("argument of pragma% must be subprogram or access type",
                   Arg2);
-               Subp := Empty;
             end if;
 
             --  ISO C requires a named parameter before the ellipsis, so a
@@ -18641,7 +18640,6 @@ package body Sem_Prag is
                     Interrupt_States.Table (IST_Num).Pragma_Loc;
                   Error_Pragma_Arg
                     ("state conflicts with that given #", Arg2);
-                  exit;
                end if;
 
                IST_Num := IST_Num + 1;
@@ -23762,7 +23760,6 @@ package body Sem_Prag is
 
                   else
                      Pragma_Misplaced;
-                     exit;
                   end if;
 
                   Prev (Stmt);

gcc/ada/sfn_scan.adb

@@ -622,7 +622,6 @@ package body SFN_Scan is
          Q := '%';
       else
          Error ("bad string");
-         Q := '"';
       end if;
 
       --  Scan out the string, B points to first char