maint: port --enable-gcc-warnings to clang

* configure.ac: If clang, add -Wno-format-extra-args and
-Wno-tautological-constant-out-of-range-compare.
* gl/lib/rand-isaac.c (ind):
* gl/lib/randread.c (readisaac):
* src/ls.c (dev_ino_push, dev_ino_pop):
* src/sort.c (buffer_linelim):
* src/system.h (is_nul):
* src/tail.c (tail_forever_inotify):
Rewrite to avoid casts that clang dislikes.
It's good to avoid casts anyway.
* src/expr.c (integer_overflow): Declare only if it exists.
(die): Remove; unused.
* src/ls.c (dev_ino_push): New function, replacing ...
(DEV_INO_PUSH): ... this removed macro.  All uses changed.
(decode_switches): Rewrite "str"+i to &str[i].

1 files changed, 7 insertions, 4 deletions

diff --git a/src/system.h b/src/system.h
index 94c968fbd..db8931635 100644
--- a/src/system.h
+++ b/src/system.h
@@ -496,21 +496,24 @@ ptr_align (void const *ptr, size_t alignment)
    Note the word after the buffer must be non NUL. */
 
 static inline bool _GL_ATTRIBUTE_PURE
-is_nul (const char *buf, size_t bufsize)
+is_nul (void const *buf, size_t bufsize)
 {
   typedef uintptr_t word;
+  void const *vp;
+  char const *cbuf = buf;
+  word const *wp = buf;
 
   /* Find first nonzero *word*, or the word with the sentinel.  */
-  word *wp = (word *) buf;
   while (*wp++ == 0)
     continue;
 
   /* Find the first nonzero *byte*, or the sentinel.  */
-  char *cp = (char *) (wp - 1);
+  vp = wp - 1;
+  char const *cp = vp;
   while (*cp++ == 0)
     continue;
 
-  return cp > buf + bufsize;
+  return cbuf + bufsize < cp;
 }
 
 /* If 10*Accum + Digit_val is larger than the maximum value for Type,