maint: avoid -Werror=strict-overflow warnings with GCC 5

All warnings were of the form: "assuming signed overflow does not occur
when simplifying conditional to constant [-Werror=strict-overflow]"

* src/dd.c (cache_round): Use an appropriately sized unsigned type,
to avoid possibility of undefined signed overflow.
* src/mknod.c (main): Likewise.
* src/pr.c (pad_down): Likewise.
* src/wc.c (main): Likewise.
* src/tail.c (main): Assert that argc >= 0 thus allowing the
compiler to assume without implication that argc - optind
is positive.

1 files changed, 2 insertions, 0 deletions

diff --git a/src/tail.c b/src/tail.c
index f75d7a9ee..b29dab1c9 100644
--- a/src/tail.c
+++ b/src/tail.c
@@ -2180,6 +2180,8 @@ main (int argc, char **argv)
         --n_units;
     }
 
+  IF_LINT (assert (0 <= argc));
+
   if (optind < argc)
     {
       n_files = argc - optind;