ada: Reject misplaced pragma Obsolescent

Pragma Obsolescent appearing before declaration was putting the
Obsolescent flag on the Standard package, which is certainly wrong. The
problem was that we relied on the Find_Lib_Unit_Name routine without
sanitizing the pragma placement with Check_Valid_Library_Unit_Pragma.

Part of cleaning up the warnings machinery to better handle references
to unset objects.

gcc/ada/

	* sem_prag.adb (Analyze_Pragma [Pragma_Obsolescent]): Reject
	misplaced pragma.

1 files changed, 8 insertions, 2 deletions

diff --git a/gcc/ada/sem_prag.adb b/gcc/ada/sem_prag.adb
index 60ea681001a..471ef870fa7 100644
--- a/gcc/ada/sem_prag.adb
+++ b/gcc/ada/sem_prag.adb
@@ -20502,10 +20502,16 @@ package body Sem_Prag is
 
             if No (Decl) then
 
-               --  First case: library level compilation unit declaration with
+               --  Case 0: library level compilation unit declaration with
+               --  the pragma preceding the declaration.
+
+               if Nkind (Parent (N)) = N_Compilation_Unit then
+                  Pragma_Misplaced;
+
+               --  Case 1: library level compilation unit declaration with
                --  the pragma immediately following the declaration.
 
-               if Nkind (Parent (N)) = N_Compilation_Unit_Aux then
+               elsif Nkind (Parent (N)) = N_Compilation_Unit_Aux then
                   Set_Obsolescent
                     (Defining_Entity (Unit (Parent (Parent (N)))));
                   return;