[gcc r12-1463] [Ada] Disable certain checks in predefined units

[gcc r12-1463] [Ada] Disable certain checks in predefined units

[Pierre-Marie de Rodat]

https://gcc.gnu.org/g:d31c2b94331ea634e58a6bf9ce93241531819380

commit r12-1463-gd31c2b94331ea634e58a6bf9ce93241531819380
Author: Bob Duff <duff@adacore.com>
Date:   Tue Feb 9 14:23:37 2021 -0500

    [Ada] Disable certain checks in predefined units
    
    gcc/ada/
    
            * sem_cat.adb (Check_Non_Static_Default_Expr): Allow nonstatic
            expression in predefined unit with pragma Preelaborate.

Diff:
---
 gcc/ada/sem_cat.adb | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/gcc/ada/sem_cat.adb b/gcc/ada/sem_cat.adb
index dc07f7897ae..92aa7ecadf5 100644
--- a/gcc/ada/sem_cat.adb
+++ b/gcc/ada/sem_cat.adb
@@ -356,6 +356,14 @@ package body Sem_Cat is
          if Present (Expression (Component_Decl))
            and then Nkind (Expression (Component_Decl)) /= N_Null
            and then not Is_OK_Static_Expression (Expression (Component_Decl))
+
+           --  If we're in a predefined unit, we can put whatever we like in a
+           --  preelaborated package, and in fact in some cases it's necessary
+           --  to bend the rules. Ada.Containers.Bounded_Hashed_Maps contains
+           --  some code that would not be considered preelaborable in user
+           --  code, for example.
+
+           and then not In_Predefined_Unit (Component_Decl)
          then
             Error_Msg_Sloc := Sloc (Component_Decl);
             Error_Msg_F