build: update to latest gnulib and adapt

* tests/binary: Reverse arguments to compare to avoid failure of
new syntax-check rule.
* configure.ac: Use -Wno-format-nonliteral.
Mark functions as pure of const, per recommendations enabled by
new gcc -W options.  Use _GL_ATTRIBUTE_PURE and _GL_ATTRIBUTE_CONST.
* lib/cmpbuf.h (buffer_lcm, block_compare):
Apply pure and/or const attributes.
* src/cmp.c (block_compare): Likewise.
* src/context.c (find_hunk): Likewise.
* src/diff.h (lines_differ): Likewise.
* src/diff3.c (skipwhite): Likewise.
* src/dir.c (dir_loop): Likewise.
* src/util.c (find_change, find_reverse_change): Likewise.
(translate_line_number): Likewise.

configure.ac

@@ -96,6 +96,7 @@ if test "$gl_gcc_warnings" = yes; then
   gl_WARN_ADD([-Wno-sign-compare])     # Too many warnings for now
   gl_WARN_ADD([-Wno-pointer-sign])     # Too many warnings for now
   gl_WARN_ADD([-Wno-unused-parameter]) # Too many warnings for now
+  gl_WARN_ADD([-Wno-format-nonliteral])
 
   # In spite of excluding -Wlogical-op above, it is enabled, as of
   # gcc 4.5.0 20090517, and it provokes warnings in cat.c, dd.c, truncate.c

gnulib

@@ -1 +1 @@
-Subproject commit 996ce97a8f8572ae9bade6c7df1aa364bd0e259f
+Subproject commit 443bc5ffcf7429e557f4a371b0661abe98ddbc13

lib/cmpbuf.h

@@ -16,4 +16,4 @@
    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
 
 size_t block_read (int, char *, size_t);
-size_t buffer_lcm (size_t, size_t, size_t);
+size_t buffer_lcm (size_t, size_t, size_t) _GL_ATTRIBUTE_CONST;

src/cmp.c

@@ -51,7 +51,7 @@
 
 static int cmp (void);
 static off_t file_position (int);
-static size_t block_compare (word const *, word const *);
+static size_t block_compare (word const *, word const *) _GL_ATTRIBUTE_PURE;
 static size_t block_compare_and_count (word const *, word const *, off_t *);
 static void sprintc (char *, unsigned char);
 

src/context.c

@@ -394,7 +394,7 @@ pr_unidiff_hunk (struct change *hunk)
    2*CONTEXT unchanged lines appear, and return a pointer
    to the `struct change' for the last change before those lines.  */
 
-static struct change *
+static struct change * _GL_ATTRIBUTE_PURE
 find_hunk (struct change *start)
 {
   struct change *prev;

src/diff.h

@@ -361,7 +361,7 @@ extern void print_sdiff_script (struct change *);
 extern char const change_letter[4];
 extern char const pr_program[];
 extern char *concat (char const *, char const *, char const *);
-extern bool lines_differ (char const *, char const *);
+extern bool lines_differ (char const *, char const *) _GL_ATTRIBUTE_PURE;
 extern lin translate_line_number (struct file_data const *, lin);
 extern struct change *find_change (struct change *);
 extern struct change *find_reverse_change (struct change *);

src/diff3.c

@@ -1045,7 +1045,7 @@ process_diff (char const *filea,
 
 /* Skip tabs and spaces, and return the first character after them.  */
 
-static char *
+static char * _GL_ATTRIBUTE_PURE
 skipwhite (char *s)
 {
   while (*s == ' ' || *s == '\t')

src/dir.c

@@ -308,7 +308,7 @@ diff_dirs (struct comparison const *cmp,
 
 /* Return nonzero if CMP is looping recursively in argument I.  */
 
-static bool
+static bool _GL_ATTRIBUTE_PURE
 dir_loop (struct comparison const *cmp, int i)
 {
   struct comparison const *p = cmp;

src/util.c

@@ -477,13 +477,13 @@ lines_differ (char const *s1, char const *s2)
 /* Find the consecutive changes at the start of the script START.
    Return the last link before the first gap.  */
 
-struct change *
+struct change * _GL_ATTRIBUTE_CONST
 find_change (struct change *start)
 {
   return start;
 }
 
-struct change *
+struct change * _GL_ATTRIBUTE_CONST
 find_reverse_change (struct change *start)
 {
   return start;
@@ -635,7 +635,7 @@ char const change_letter[] = { 0, 'd', 'a', 'c' };
    Internal line numbers count from 0 starting after the prefix.
    Actual line numbers count from 1 within the entire file.  */
 
-lin
+lin _GL_ATTRIBUTE_PURE
 translate_line_number (struct file_data const *file, lin i)
 {
   return i + file->prefix_lines + 1;

tests/binary

@@ -11,7 +11,7 @@ printf '\0'|diff - /dev/null > out 2> err
 
 # diff must exit with status 2, stdout as above, and no stderr.
 test $? = 2 || fail=1
-compare out out-exp || fail=1
+compare out-exp out || fail=1
 compare /dev/null err || fail=1
 
 Exit $fail