Add missing sentinel 'char *' casts in concat/reconcat calls

The wildebeest-debian-wheezy-i686 buildslave's build is broken due to:

 ../../binutils-gdb/gdb/python/python.c: In function void _initialize_python():
 ../../binutils-gdb/gdb/python/python.c:1709:36: error: missing sentinel in function call [-Werror=format]

Reproduced on Fedora 23 by sticking a few:

 #undef NULL
 #define 0

in build/gdb/build-gnulib/{stddef|signal|stdio}.h.  Hopefully this
caught all instances.

gdb/ChangeLog:
2016-04-21  Pedro Alves  <palves@redhat.com>

	* dwarf2read.c (try_open_dwop_file, open_dwo_file)
	(file_file_name, file_full_name): Add char * cast to sentinel in
	concat/reconcat calls.
	* event-top.c (top_level_prompt): Likewise.
	* guile/guile.c (initialize_scheme_side): Likewise.
	* linux-tdep.c (linux_fill_prpsinfo): Likewise.
	* macrotab.c (macro_source_fullname): Likewise.
	* main.c (get_init_files, captured_main): Likewise.
	* psymtab.c (psymtab_to_fullname): Likewise.
	* python/python.c (_initialize_python)
	(gdbpy_finish_initialization): Likewise.
	* source.c (symtab_to_fullname): Likewise.

gdb/ChangeLog

@@ -1,3 +1,18 @@
+2016-04-21  Pedro Alves  <palves@redhat.com>
+
+	* dwarf2read.c (try_open_dwop_file, open_dwo_file)
+	(file_file_name, file_full_name): Add char * cast to sentinel in
+	concat/reconcat calls.
+	* event-top.c (top_level_prompt): Likewise.
+	* guile/guile.c (initialize_scheme_side): Likewise.
+	* linux-tdep.c (linux_fill_prpsinfo): Likewise.
+	* macrotab.c (macro_source_fullname): Likewise.
+	* main.c (get_init_files, captured_main): Likewise.
+	* psymtab.c (psymtab_to_fullname): Likewise.
+	* python/python.c (_initialize_python)
+	(gdbpy_finish_initialization): Likewise.
+	* source.c (symtab_to_fullname): Likewise.
+
 2016-04-20  Pedro Alves  <palves@redhat.com>
 
 	* build-with-cxx.m4 (GDB_AC_BUILD_WITH_CXX): Default to yes.

gdb/dwarf2read.c

@@ -10482,7 +10482,7 @@ try_open_dwop_file (const char *file_name, int is_dwp, int search_cwd)
     {
       if (*debug_file_directory != '\0')
 	search_path = concat (".", dirname_separator_string,
-			      debug_file_directory, NULL);
+			      debug_file_directory, (char *) NULL);
       else
 	search_path = xstrdup (".");
     }
@@ -10538,7 +10538,8 @@ open_dwo_file (const char *file_name, const char *comp_dir)
 
   if (comp_dir != NULL)
     {
-      char *path_to_try = concat (comp_dir, SLASH_STRING, file_name, NULL);
+      char *path_to_try = concat (comp_dir, SLASH_STRING,
+				  file_name, (char *) NULL);
 
       /* NOTE: If comp_dir is a relative path, this will also try the
 	 search path, which seems useful.  */
@@ -20871,7 +20872,7 @@ file_file_name (int file, struct line_header *lh)
 	  || lh->include_dirs == NULL)
         return xstrdup (fe->name);
       return concat (lh->include_dirs[fe->dir_index - 1], SLASH_STRING,
-		     fe->name, NULL);
+		     fe->name, (char *) NULL);
     }
   else
     {
@@ -20906,7 +20907,8 @@ file_full_name (int file, struct line_header *lh, const char *comp_dir)
 
       if (IS_ABSOLUTE_PATH (relative) || comp_dir == NULL)
 	return relative;
-      return reconcat (relative, comp_dir, SLASH_STRING, relative, NULL);
+      return reconcat (relative, comp_dir, SLASH_STRING,
+		       relative, (char *) NULL);
     }
   else
     return file_file_name (file, lh);

gdb/event-top.c

@@ -364,7 +364,7 @@ top_level_prompt (void)
 	 beginning.  */
       const char suffix[] = "\n\032\032prompt\n";
 
-      return concat (prefix, prompt, suffix, NULL);
+      return concat (prefix, prompt, suffix, (char *) NULL);
     }
 
   return xstrdup (prompt);

gdb/guile/guile.c

@@ -628,9 +628,9 @@ initialize_scheme_side (void)
   char *boot_scm_path;
   char *msg;
 
-  guile_datadir = concat (gdb_datadir, SLASH_STRING, "guile", NULL);
+  guile_datadir = concat (gdb_datadir, SLASH_STRING, "guile", (char *) NULL);
   boot_scm_path = concat (guile_datadir, SLASH_STRING, "gdb",
-			  SLASH_STRING, boot_scm_filename, NULL);
+			  SLASH_STRING, boot_scm_filename, (char *) NULL);
 
   scm_c_catch (SCM_BOOL_T, boot_guile_support, boot_scm_path,
 	       handle_boot_error, boot_scm_path, NULL, NULL);

gdb/linux-tdep.c

@@ -1789,7 +1789,7 @@ linux_fill_prpsinfo (struct elf_internal_linux_prpsinfo *p)
 
   psargs = xstrdup (fname);
   if (infargs != NULL)
-    psargs = reconcat (psargs, psargs, " ", infargs, NULL);
+    psargs = reconcat (psargs, psargs, " ", infargs, (char *) NULL);
 
   make_cleanup (xfree, psargs);
 

gdb/macrotab.c

@@ -1102,5 +1102,5 @@ macro_source_fullname (struct macro_source_file *file)
   if (comp_dir == NULL || IS_ABSOLUTE_PATH (file->filename))
     return xstrdup (file->filename);
 
-  return concat (comp_dir, SLASH_STRING, file->filename, NULL);
+  return concat (comp_dir, SLASH_STRING, file->filename, (char *) NULL);
 }

gdb/main.c

@@ -232,7 +232,7 @@ get_init_files (const char **system_gdbinit,
 	      for (p = tmp_sys_gdbinit; IS_DIR_SEPARATOR (*p); ++p)
 		continue;
 	      relocated_sysgdbinit = concat (gdb_datadir, SLASH_STRING, p,
-					     NULL);
+					     (char *) NULL);
 	      xfree (tmp_sys_gdbinit);
 	    }
 	  else
@@ -560,7 +560,7 @@ captured_main (void *data)
 #ifdef WITH_PYTHON_PATH
   {
     /* For later use in helping Python find itself.  */
-    char *tmp = concat (WITH_PYTHON_PATH, SLASH_STRING, "lib", NULL);
+    char *tmp = concat (WITH_PYTHON_PATH, SLASH_STRING, "lib", (char *) NULL);
 
     python_libdir = relocate_gdb_directory (tmp, PYTHON_PATH_RELOCATABLE);
     xfree (tmp);

gdb/psymtab.c

@@ -1224,7 +1224,8 @@ psymtab_to_fullname (struct partial_symtab *ps)
 	  if (ps->dirname == NULL || IS_ABSOLUTE_PATH (ps->filename))
 	    fullname = xstrdup (ps->filename);
 	  else
-	    fullname = concat (ps->dirname, SLASH_STRING, ps->filename, NULL);
+	    fullname = concat (ps->dirname, SLASH_STRING,
+			       ps->filename, (char *) NULL);
 
 	  back_to = make_cleanup (xfree, fullname);
 	  ps->fullname = rewrite_source_path (fullname);

gdb/python/python.c

@@ -1706,7 +1706,7 @@ message == an error message without a stack will be printed."),
      /foo/lib/pythonX.Y/...
      This must be done before calling Py_Initialize.  */
   progname = concat (ldirname (python_libdir), SLASH_STRING, "bin",
-		     SLASH_STRING, "python", NULL);
+		     SLASH_STRING, "python", (char *) NULL);
 #ifdef IS_PY3K
   oldloc = setlocale (LC_ALL, NULL);
   setlocale (LC_ALL, "");
@@ -1881,7 +1881,7 @@ gdbpy_finish_initialization (const struct extension_language_defn *extlang)
 
   /* Add the initial data-directory to sys.path.  */
 
-  gdb_pythondir = concat (gdb_datadir, SLASH_STRING, "python", NULL);
+  gdb_pythondir = concat (gdb_datadir, SLASH_STRING, "python", (char *) NULL);
   make_cleanup (xfree, gdb_pythondir);
 
   sys_path = PySys_GetObject ("path");

gdb/source.c

@@ -1178,8 +1178,8 @@ symtab_to_fullname (struct symtab *s)
 	  if (SYMTAB_DIRNAME (s) == NULL || IS_ABSOLUTE_PATH (s->filename))
 	    fullname = xstrdup (s->filename);
 	  else
-	    fullname = concat (SYMTAB_DIRNAME (s), SLASH_STRING, s->filename,
+	    fullname = concat (SYMTAB_DIRNAME (s), SLASH_STRING,
-			       NULL);
+			       s->filename, (char *) NULL);
 
 	  back_to = make_cleanup (xfree, fullname);
 	  s->fullname = rewrite_source_path (fullname);