[Ada] Introduce -gnatd_A to set Opt.Disable_ALI_File

This will allow us to remove the import of flag_compare_debug in
lib-writ.adb in a second stage.

2018-09-26  Arnaud Charlet  <charlet@adacore.com>

gcc/ada/

	* gnat1drv.adb (Adjust_Global_Switches): -gnatd_A sets
	Opt.Disable_ALI_File.
	* debug.adb: Update debug flags documentation.

From-SVN: r264605

gcc/ada/ChangeLog

@@ -1,3 +1,9 @@
+2018-09-26  Arnaud Charlet  <charlet@adacore.com>
+
+	* gnat1drv.adb (Adjust_Global_Switches): -gnatd_A sets
+	Opt.Disable_ALI_File.
+	* debug.adb: Update debug flags documentation.
+
 2018-09-26  Ed Schonberg  <schonberg@adacore.com>
 
 	* contracts.adb (Analyze_Entry_Or_Subprogram_Contract): The

gcc/ada/debug.adb

@@ -172,7 +172,7 @@ package body Debug is
    --  d_y
    --  d_z
 
-   --  d_A
+   --  d_A  Stop generation of ALI file
    --  d_B
    --  d_C
    --  d_D
@@ -843,6 +843,8 @@ package body Debug is
    --       a call to routine Ada.Synchronous_Task_Control.Suspend_Until_True
    --       or Ada.Synchronous_Barriers.Wait_For_Release.
 
+   --  d_A  Do not generate ALI files by setting Opt.Disable_ALI_File.
+
    --  d_L  Output trace information on elaboration checking. This debug switch
    --       causes output to be generated showing each call or instantiation as
    --       it is checked, and the progress of the recursive trace through

gcc/ada/gnat1drv.adb

@@ -161,6 +161,12 @@ procedure Gnat1drv is
          Modify_Tree_For_C := True;
       end if;
 
+      --  -gnatd_A disables generation of ALI files.
+
+      if Debug_Flag_Underscore_AA then
+         Disable_ALI_File := True;
+      end if;
+
       --  Set all flags required when generating C code
 
       if Generate_C_Code then