[x]concat-filename: Improve GCC 11 allocation-deallocation checking

[Bruno Haible]

2021-08-07  Bruno Haible  <br...@clisp.org>

        [x]concat-filename: Improve GCC 11 allocation-deallocation checking.
        * lib/concat-filename.h: Include <stdlib.h>.
        (concatenated_filename, xconcatenated_filename): Declare that
        deallocation must happen through 'free'.

diff --git a/lib/concat-filename.h b/lib/concat-filename.h
index 5a7d393..32a437e 100644
--- a/lib/concat-filename.h
+++ b/lib/concat-filename.h
@@ -17,6 +17,8 @@
 #ifndef _CONCAT_FILENAME_H
 #define _CONCAT_FILENAME_H
 
+#include <stdlib.h>
+
 #ifdef __cplusplus
 extern "C" {
 #endif
@@ -26,12 +28,15 @@ extern "C" {
    suffix.  Return a freshly allocated filename.  Return NULL and set errno
    upon memory allocation failure.  */
 extern char *concatenated_filename (const char *directory,
-                                    const char *filename, const char *suffix);
+                                    const char *filename, const char *suffix)
+  _GL_ATTRIBUTE_MALLOC _GL_ATTRIBUTE_DEALLOC_FREE;
 
 /* Concatenate a directory filename, a relative filename and an optional
    suffix.  Return a freshly allocated filename.  */
 extern char *xconcatenated_filename (const char *directory,
-                                     const char *filename, const char *suffix);
+                                     const char *filename, const char *suffix)
+  _GL_ATTRIBUTE_MALLOC _GL_ATTRIBUTE_DEALLOC_FREE
+  _GL_ATTRIBUTE_RETURNS_NONNULL;
 
 
 #ifdef __cplusplus