build: avoid a warning form gcc's new -Wlogical-op

Without this change, very recent gcc (e.g., version 6.0.0 20150509)
would print the following when configured with --enable-gcc-warnings:

  src/copy.c:165:30: error: logical 'or' of equal expressions \
    [-Werror=logical-op]
    && (errno == EOPNOTSUPP || errno == ENOTSUP || errno == ENOSYS))
                           ^
* src/system.h (is_ENOTSUP): New function.
* src/copy.c (punch_hole): Use it.
* src/ls.c (errno_unsupported, gobble_file): Use it.

1 files changed, 14 insertions, 0 deletions

diff --git a/src/system.h b/src/system.h
index c55f6d8bd..0e25bc414 100644
--- a/src/system.h
+++ b/src/system.h
@@ -695,3 +695,17 @@ stzncpy (char *restrict dest, char const *restrict src, size_t len)
    in selinux.h before libselinux-2.3 (May 2014).
    When version >= 2.3 is ubiquitous remove this function.  */
 static inline char * se_const (char const * sctx) { return (char *) sctx; }
+
+/* Return true if ERR is ENOTSUP or EOPNOTSUPP, otherwise false.
+   This wrapper function avoids the redundant 'or'd comparison on
+   systems like Linux for which they have the same value.  It also
+   avoids the gcc warning to that effect.  */
+static inline bool
+is_ENOTSUP (int err)
+{
+  return err == EOPNOTSUPP
+#if ENOTSUP != EOPNOTSUPP
+    || err == ENOTSUP
+#endif
+    ;
+}