[Ada] Do not generate .ali files for subunits

[Arnaud Charlet]

This patch fixes a bug in which the compiler creates .ali files when a
subunit is compiled. Given the following code:

package P is
  procedure F;
end P;

package body P is
  procedure F is separate;
end P;

separate (P)
procedure F is
begin
  null;
end F;

The command:

gcc -c p-f.adb

should generate an error:

cannot generate code for file p-f.adb (subunit)

and p-f.ali should not be created.

Tested on x86_64-pc-linux-gnu, committed on trunk

2017-09-08  Bob Duff  <duff@adacore.com>

	* gnat1drv.adb (Gnat1drv): Do not set the Force_ALI_Tree_File flag in
	the subunit case. It's still OK to set it in the "missing subunits"
	case, because that won't cause the obsolete .ali files that cause
	confusion.

-------------- next part --------------
Index: gnat1drv.adb
===================================================================
--- gnat1drv.adb	(revision 251863)
+++ gnat1drv.adb	(working copy)
@@ -1353,10 +1353,10 @@
                Write_Str (" (subunit)");
                Write_Eol;
 
-               --  Force generation of ALI file, for backward compatibility
+               --  Do not generate an ALI file in this case, because it would
+               --  become obsolete when the parent is compiled, and thus
+               --  confuse tools such as gnatfind.
 
-               Opt.Force_ALI_Tree_File := True;
-
             elsif Main_Unit_Kind = N_Subprogram_Declaration then
                Write_Str (" (subprogram spec)");
                Write_Eol;