1) Add FreeBSD: tag.
2) Add parenthesis around macro args.
3) Add parenthesis around macros which are expressions.
4) Add do { ... } while (0) around macros which are compound statements.
5) Sync bitstr_size and bit_alloc with neater versions from NetBSD.
6) Fix bit_ffs and bit_ffc so that they don't search off the end of the
bitstirng.
7) Try to avoid rightshifting signed ints.
I didn't take NetBSD's version directly as the macros are significantly
slower for long bitstrings. Bruce reviewed a previous version of
this patch.
PR: 21204
Submitted by: bob@immure.com
Reviewed by: bde
