MFC r268642:

MFC	r268642:
libc/gen: small updates to code originating at OpenBSD

arc4random.c
- CVS rev. 1.22
Change arc4random_uniform() to calculate ``2**32 % upper_bound'' as
``-upper_bound % upper_bound''. Simplifies the code and makes it the
same on both ILP32 and LP64 architectures, and also slightly faster on
LP64 architectures by using a 32-bit remainder instead of a 64-bit
remainder.
- CVS rev. 1.23
Spacing

readpassphrase.c
-CVS rev. v 1.24
most obvious unsigned char casts for ctype

Obtained from:	OpenBSD

git-svn-id: svn://svn.freebsd.org/base/stable/10@268962 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f