libbsd: needs __register_atfork

libbsd: needs __register_atfork

The following error is raised by minizip:

[100%] Linking C executable minizip
/home/peko/autobuild/instance-0/output/host/m68k-buildroot-uclinux-uclibc/sysroot/usr/lib/libbsd.a(arc4random.o):
In function `_rs_init.part.1':
arc4random.c:(.text+0xaa): undefined reference to `__register_atfork'
collect2: error: ld returned 1 exit status

As specified in openssl/Config.in, uClibc on noMMU doesn't provide
__register_atfork() so add a dependency on
!(BR2_TOOLCHAIN_USES_UCLIBC && !BR2_USE_MMU) on libbsd and minizip

Don't add this dependency to netcat-opensd as it already depends on
glibc
Don't add this dependency to BR2_PACKAGE_BLUEZ_ALSA_HCITOP because
bluez-alsa already depends on BR2_USE_MMU
Concerning fwts, just update comment on BR2_USE_MMU

Fixes:
 - http://autobuild.buildroot.org/results/df2dcbdceaa01a2ae37bf09140e4dbef0a5b9489

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>