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>
diff --git a/util-linux/fsfreeze.c b/util-linux/fsfreeze.c
index 6e2ff0a..fb0b3c4 100644
--- a/util-linux/fsfreeze.c
+++ b/util-linux/fsfreeze.c
@@ -7,6 +7,7 @@
 //config:config FSFREEZE
 //config:	bool "fsfreeze (3.5 kb)"
 //config:	default y
+//config:	select PLATFORM_LINUX
 //config:	select LONG_OPTS
 //config:	help
 //config:	Halt new accesses and flush writes on a mounted filesystem.