[Ada] Clean up scanner

This patch removes some obsolete code in the scanner and related files,
and corrects some comments. Tok_Special is used only by the
preprocessor, and uses only the two characters '#' and '$'.

It might be simpler to have a single flag indicating we're scanning for
preprocessing, instead of the Special_Characters array and the
End_Of_Line_Is_Token flag, but that's for another day.

gcc/ada/

	* scans.ads: Fix obsolete comments about Tok_Special, and give
	Special_Character a predicate assuring it is one of the two
	characters used in preprocessing.
	* scng.ads: Clean up comments.
	* scng.adb: Clean up handling of Tok_Special.  Remove comment
	about '@' (target_name), which doesn't seem very helpful.
	Set_Special_Character will now blow up if given anything other
	than '#' and '$', because of the predicate on Special_Character;
	it's not clear why it used to say "when others => null;".
	Remove Comment_Is_Token, which is not used.
	* scn.ads: Remove commented-out use clause.  Remove redundant
	comment.
	* ali-util.adb: Use "is null" for do-nothing procedures.
	* gprep.adb (Post_Scan): Use "is null".

1 files changed, 5 insertions, 58 deletions

diff --git a/gcc/ada/ali-util.adb b/gcc/ada/ali-util.adb
index bb1fc41..6435905 100644
--- a/gcc/ada/ali-util.adb
+++ b/gcc/ada/ali-util.adb
@@ -42,15 +42,12 @@ package body ALI.Util is
    --  empty, because we don't want to report any errors when computing
    --  a source checksum.
 
-   procedure Post_Scan;
+   procedure Post_Scan is null;
 
-   procedure Error_Msg (Msg : String; Flag_Location : Source_Ptr);
-
-   procedure Error_Msg_S (Msg : String);
-
-   procedure Error_Msg_SC (Msg : String);
-
-   procedure Error_Msg_SP (Msg : String);
+   procedure Error_Msg (Msg : String; Flag_Location : Source_Ptr) is null;
+   procedure Error_Msg_S (Msg : String) is null;
+   procedure Error_Msg_SC (Msg : String) is null;
+   procedure Error_Msg_SP (Msg : String) is null;
 
    --  Instantiation of Styleg, needed to instantiate Scng
 
@@ -85,47 +82,6 @@ package body ALI.Util is
       return Checksum1 = Checksum2 and then Checksum1 /= Checksum_Error;
    end Checksums_Match;
 
-   ---------------
-   -- Error_Msg --
-   ---------------
-
-   procedure Error_Msg (Msg : String; Flag_Location : Source_Ptr) is
-      pragma Warnings (Off, Msg);
-      pragma Warnings (Off, Flag_Location);
-   begin
-      null;
-   end Error_Msg;
-
-   -----------------
-   -- Error_Msg_S --
-   -----------------
-
-   procedure Error_Msg_S (Msg : String) is
-      pragma Warnings (Off, Msg);
-   begin
-      null;
-   end Error_Msg_S;
-
-   ------------------
-   -- Error_Msg_SC --
-   ------------------
-
-   procedure Error_Msg_SC (Msg : String) is
-      pragma Warnings (Off, Msg);
-   begin
-      null;
-   end Error_Msg_SC;
-
-   ------------------
-   -- Error_Msg_SP --
-   ------------------
-
-   procedure Error_Msg_SP (Msg : String) is
-      pragma Warnings (Off, Msg);
-   begin
-      null;
-   end Error_Msg_SP;
-
    -----------------------
    -- Get_File_Checksum --
    -----------------------
@@ -192,15 +148,6 @@ package body ALI.Util is
       Interfaces.Reset;
    end Initialize_ALI_Source;
 
-   ---------------
-   -- Post_Scan --
-   ---------------
-
-   procedure Post_Scan is
-   begin
-      null;
-   end Post_Scan;
-
    ----------------------
    -- Read_Withed_ALIs --
    ----------------------