[Ada] Fix crash on invalid `pragma Profile`

[Pierre-Marie de Rodat]

Before this commit, GNAT would crash when encountering uses of the
`Profile` pragma that did not have an identifier as argument (e.g.
`pragma Profile("a")`).

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

gcc/ada/

        * sem_prag.adb (Analyze_Pragma): Emit error on wrong argument
        nkind.
diff --git a/gcc/ada/sem_prag.adb b/gcc/ada/sem_prag.adb
--- a/gcc/ada/sem_prag.adb
+++ b/gcc/ada/sem_prag.adb
@@ -21494,7 +21494,11 @@ package body Sem_Prag is
                Argx : constant Node_Id := Get_Pragma_Arg (Arg1);
 
             begin
-               if Chars (Argx) = Name_Ravenscar then
+               if Nkind (Argx) /= N_Identifier then
+                  Error_Msg_N
+                    ("argument of pragma Profile must be an identifier", N);
+
+               elsif Chars (Argx) = Name_Ravenscar then
                   Set_Ravenscar_Profile (Ravenscar, N);
 
                elsif Chars (Argx) = Name_Jorvik then