[Ada] Fix crash on frontend inlining of functions with single returns

[Pierre-Marie de Rodat via Gcc-patches]

When examining expression of the first declaration of the inlined body
make sure that this declaration is in fact an object declaration.

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

gcc/ada/

        * inline.adb (Has_Single_Return): Add guard for the subsequent
        call to Expression.
diff --git a/gcc/ada/inline.adb b/gcc/ada/inline.adb
--- a/gcc/ada/inline.adb
+++ b/gcc/ada/inline.adb
@@ -4648,6 +4648,7 @@ package body Inline is
          return
            Present (Declarations (N))
              and then Present (First (Declarations (N)))
+             and then Nkind (First (Declarations (N))) = N_Object_Declaration
              and then Entity (Expression (Return_Statement)) =
                         Defining_Identifier (First (Declarations (N)));
       end if;