[Ada] Internal error compiling formal instance of generic with Initial_Condition

[Marc Poulhiès via Gcc-patches]

Prevent the compiler from failing with an internal error in some cases involving
an instance of a generic which takes as a formal parameter an instance of a
second generic, where the second generic has an Initial_Condition aspect
specification.

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

gcc/ada/

        * contracts.adb
        (Analyze_Package_Contract): Do not analyze the contract of a
        temporary package created just to check conformance of an actual
        package.
diff --git a/gcc/ada/contracts.adb b/gcc/ada/contracts.adb
--- a/gcc/ada/contracts.adb
+++ b/gcc/ada/contracts.adb
@@ -1319,6 +1319,18 @@ package body Contracts is
       if Present (Items) then
          if Analyzed (Items) then
             return;
+
+         --  Do not analyze the contract of the internal package
+         --  created to check conformance of an actual package.
+         --  Such an internal package is removed from the tree after
+         --  legality checks are completed, and it does not contain
+         --  the declarations of all local entities of the generic.
+
+         elsif Is_Internal (Pack_Id)
+           and then Is_Generic_Instance (Pack_Id)
+         then
+            return;
+
          else
             Set_Analyzed (Items);
          end if;