Fix non-Linux builds

Various tools are Linuxish and should thus only attempted to build on
Linux only. Some features are also Linux-only.

Also, libresolv is used on all GNU platforms, notably GNU/Hurd and
GNU/kfreeBSD.

Signed-off-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

sysklogd/klogd.c

@@ -19,6 +19,7 @@
 //config:config KLOGD
 //config:	bool "klogd (5.7 kb)"
 //config:	default y
+//config:	select PLATFORM_LINUX
 //config:	help
 //config:	klogd is a utility which intercepts and logs all
 //config:	messages from the Linux kernel and sends the messages