selftests: split out make_fndecl from selftest.h to its own header

Avoid selftest.h requiring the "tree" type.
No functional change intended.

gcc/analyzer/ChangeLog:
	* region-model.cc: Include "selftest-tree.h".

gcc/ChangeLog:
	* function-tests.cc: Include "selftest-tree.h".
	* selftest-tree.h: New file.
	* selftest.h (make_fndecl): Move to selftest-tree.h.

Signed-off-by: David Malcolm <dmalcolm@redhat.com>

gcc/analyzer/region-model.cc

@@ -42,6 +42,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "diagnostic-color.h"
 #include "bitmap.h"
 #include "selftest.h"
+#include "selftest-tree.h"
 #include "analyzer/analyzer.h"
 #include "analyzer/analyzer-logging.h"
 #include "ordered-hash-map.h"

gcc/function-tests.cc

@@ -76,6 +76,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "ipa-ref.h"
 #include "cgraph.h"
 #include "selftest.h"
+#include "selftest-tree.h"
 #include "print-rtl.h"
 
 #if CHECKING_P

gcc/selftest-tree.h

@@ -0,0 +1,41 @@
+/* A self-testing framework, for use by -fself-test.
+   Copyright (C) 2015-2024 Free Software Foundation, Inc.
+
+This file is part of GCC.
+
+GCC is free software; you can redistribute it and/or modify it under
+the terms of the GNU General Public License as published by the Free
+Software Foundation; either version 3, or (at your option) any later
+version.
+
+GCC is distributed in the hope that it will be useful, but WITHOUT ANY
+WARRANTY; without even the implied warranty of MERCHANTABILITY or
+FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+for more details.
+
+You should have received a copy of the GNU General Public License
+along with GCC; see the file COPYING3.  If not see
+<http://www.gnu.org/licenses/>.  */
+
+#ifndef GCC_SELFTEST_TREE_H
+#define GCC_SELFTEST_TREE_H
+
+/* The selftest code should entirely disappear in a production
+   configuration, hence we guard all of it with #if CHECKING_P.  */
+
+#if CHECKING_P
+
+namespace selftest {
+
+/* Helper function for selftests that need a function decl.  */
+
+extern tree make_fndecl (tree return_type,
+			 const char *name,
+			 vec <tree> &param_types,
+			 bool is_variadic = false);
+
+} /* end of namespace selftest.  */
+
+#endif /* #if CHECKING_P */
+
+#endif /* GCC_SELFTEST_TREE_H */

gcc/selftest.h

@@ -178,13 +178,6 @@ class line_table_test
   ~line_table_test ();
 };
 
-/* Helper function for selftests that need a function decl.  */
-
-extern tree make_fndecl (tree return_type,
-			 const char *name,
-			 vec <tree> &param_types,
-			 bool is_variadic = false);
-
 /* Run TESTCASE multiple times, once for each case in our test matrix.  */
 
 extern void