[Bug ada/126553] New: Compiler error with -gnateV.

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126553

            Bug ID: 126553
           Summary: Compiler error with -gnateV.
           Product: gcc
           Version: 16.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: ada
          Assignee: unassigned at gcc dot gnu.org
          Reporter: p.p11 at orange dot fr
                CC: dkm at gcc dot gnu.org
  Target Milestone: ---

Created attachment 65197
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=65197&action=edit
Reproducer.

Actual behavior:
(Full source files in attached archive)

% gcc -c posix-timers.adb
# Compilation ok

% gcc -c -gnateV posix-timers.adb
+===========================GNAT BUG DETECTED==============================+
| 16.1.0 (x86_64-apple-darwin24.6.0) Constraint_Error erroneous memory access|
| Error detected at posix-timers.ads:70:13                                 |
| Compiling posix-timers.adb                          |
# Compilation error with -gnateV option.

Expected behavior:
Compilation OK with -gnateV option.

Note:
Maybe related to Bug 123857 as there is an Unchecked_Union in posix-c.ads:
570.    type sigval (Dummy : Boolean := True) is record
571.       case Dummy is
572.          when True  => sival_int : int;
573.          when False => sival_ptr : System.Address;
574.       end case;
575.    end record;
576.    pragma Unchecked_Union (sigval);