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, 3 insertions, 3 deletions

diff --git a/src/pr.c b/src/pr.c
index 78fe69799..6ff51ec5a 100644
--- a/src/pr.c
+++ b/src/pr.c
@@ -438,7 +438,7 @@ static void init_store_cols (void);
 static void store_columns (void);
 static void balance (int total_stored);
 static void store_char (char c);
-static void pad_down (int lines);
+static void pad_down (unsigned int lines);
 static void read_rest_of_line (COLUMN *p);
 static void skip_read (COLUMN *p, int column_number);
 static void print_char (char c);
@@ -2052,9 +2052,9 @@ pad_across_to (int position)
    Otherwise, use newlines. */
 
 static void
-pad_down (int lines)
+pad_down (unsigned int lines)
 {
-  int i;
+  unsigned int i;
 
   if (use_form_feed)
     putchar ('\f');