[Ada] Fix record layout warnings not being tagged

[Pierre-Marie de Rodat <derodat@adacore.com>]

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This allows tools ingesting GNAT's output to properly classify these
messages.

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

gcc/ada/

	* gcc-interface/decl.cc (warn_on_field_placement): Add insertion
	character '.q' to warning string.

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diff --git a/gcc/ada/gcc-interface/decl.cc b/gcc/ada/gcc-interface/decl.cc
--- a/gcc/ada/gcc-interface/decl.cc
+++ b/gcc/ada/gcc-interface/decl.cc
@@ -7770,20 +7770,20 @@ warn_on_field_placement (tree gnu_field, Node_Id gnat_component_list,
 
   const char *msg1
     = in_variant
-      ? "??variant layout may cause performance issues"
-      : "??record layout may cause performance issues";
+      ? "?.q?variant layout may cause performance issues"
+      : "?.q?record layout may cause performance issues";
   const char *msg2
     = Ekind (gnat_field) == E_Discriminant
-      ? "??discriminant & whose length is not multiple of a byte"
+      ? "?.q?discriminant & whose length is not multiple of a byte"
       : field_has_self_size (gnu_field)
-	? "??component & whose length depends on a discriminant"
+	? "?.q?component & whose length depends on a discriminant"
 	: field_has_variable_size (gnu_field)
-	  ? "??component & whose length is not fixed"
-	  : "??component & whose length is not multiple of a byte";
+	  ? "?.q?component & whose length is not fixed"
+	  : "?.q?component & whose length is not multiple of a byte";
   const char *msg3
     = do_reorder
-      ? "??comes too early and was moved down"
-      : "??comes too early and ought to be moved down";
+      ? "?.q?comes too early and was moved down"
+      : "?.q?comes too early and ought to be moved down";
 
   post_error (msg1, gnat_field);
   post_error_ne (msg2, gnat_field, gnat_field);