* doc/posix-functions/crypt.texi: Mention need for _GNU_SOURCE on glibc
systems.
* doc/posix-functions/encrypt.texi: Likewise.
* doc/posix-functions/setkey.texi: Likewise.
* m4/printf.m4 (gl_PRINTF_INFINITE_LONG_DOUBLE): Don't guess yes on
NetBSD; the test fails on NetBSD 5.0.
* doc/{glibc,posix,pastposix}-{headers,functions}/*.texi: Update info
about NetBSD.