warning cleanup: suspicious switch fallthrough cases.

This is the seventh round of an effort to enable GCC's -Wextra
option. Warnings about switch fallthrough situations are
addressed. GCC now has a diagnostic for this that is enabled
by -Wextra in such a way that if a fallthrough comment is
present, the diagnostic is suppressed. In much of the code,
we have such a comment. It's missing in a few places, or
misplaced. There are also some real bugs.

* hash.c (hash_buf): Add fallthrough comments to intentional
fallthrough cases.
(hash_hash_op): bugfix: add break statement. The 32 and 64
bit cases are independent (at compile time).

* lib.c (cdr, nullify, list_collect, empty): Add fallthrough
comment.
(int_str): Add missing break. This has not caused a
bug though because setting the octzero flag in the zerox
case is harmless to the logic which follows.

* linenoise.c (edit): Move misplaced fallthrough.

* sysif.c (fcntl_wrap): Bugfix: add missing break, without
which errno is tampered to hold EINVAL, in spite of a
successful F_SETLK, F_SETLKW or F_GETLK operation.

* unwind.h (jmp_restore): Declare noreturn, so that GCC
does not issue a false positive warning about a fallthrough
in uw_unwind_to_exit_point.

* utf8.c (utf8_from_buf, utf8_decode): Move a fallthrough
comment outside of preprocessing, so it is properly processed
by GCC's diagnostic.

1 files changed, 2 insertions, 2 deletions

diff --git a/utf8.c b/utf8.c
index 8afae187..9c286756 100644
--- a/utf8.c
+++ b/utf8.c
@@ -90,10 +90,10 @@ size_t utf8_from_buf(wchar_t *wdst, const unsigned char *src, size_t nbytes)
           wch_min = 0x10000;
           break;
         }
-        /* fallthrough */
 #else
         conversion_error();
 #endif
+        /* fallthrough */
       default:
         if (wdst)
           *wdst++ = 0xDC00 | ch;
@@ -321,10 +321,10 @@ wint_t utf8_decode(utf8_decoder_t *ud, int (*get)(mem_t *ctx), mem_t *ctx)
           ud->wch_min = 0x10000;
           break;
         }
-        /* fallthrough */
 #else
         conversion_error();
 #endif
+        /* fallthrough */
       default:
         ud->back = ud->tail;
         return 0xDC00 | ch;