[svn-r27165] Merge 27133 & 27158 from trunk:

- Add a new attribute function characterstic for format:
   * H5_ATTR_FORMAT(X,Y,Z)  __attribute__((format(X, Y, Z)))
 - Rename UNUSED attribute characterstic to H5_ATTR_UNUSED.
 - Rename NORETURN attribute characterstic to H5_ATTR_NORETURN

tested with h5committest.

tools/h5diff/h5diffgentest.c

@@ -106,8 +106,8 @@ hsize_t H5TOOLS_MALLOCSIZE = (128 * 1024 * 1024);
 #define SPACE1_DIM2 0
 
 /* A UD link traversal function.  Shouldn't actually be called. */
-static hid_t UD_traverse(UNUSED const char * link_name, UNUSED hid_t cur_group,
-                         UNUSED const void * udata, UNUSED size_t udata_size, UNUSED hid_t lapl_id)
+static hid_t UD_traverse(H5_ATTR_UNUSED const char * link_name, H5_ATTR_UNUSED hid_t cur_group,
+                         H5_ATTR_UNUSED const void * udata, H5_ATTR_UNUSED size_t udata_size, H5_ATTR_UNUSED hid_t lapl_id)
 {
     return -1;
 }