mark Linux-specific configuration options

PLATFORM_LINUX is used as a dependency for applets or features
which require Linux-specific interfaces.

Signed-off-by: Jeremie Koenig <jk@jk.fr.eu.org>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/Config.in b/Config.in
index eebc977..35f43b3 100644
--- a/Config.in
+++ b/Config.in
@@ -47,6 +47,17 @@
 	  compiler other than gcc.
 	  If you do use gcc, this option may needlessly increase code size.
 
+config PLATFORM_LINUX
+	bool "Enable Linux-specific applets and features"
+	default y
+	help
+	  For the most part, busybox requires only POSIX compatibility
+	  from the target system, but some applets and features use
+	  Linux-specific interfaces.
+
+	  Answering 'N' here will disable such applets and hide the
+	  corresponding configuration options.
+
 choice
 	prompt "Buffer allocation policy"
 	default FEATURE_BUFFERS_USE_MALLOC
@@ -353,6 +364,7 @@
 config SELINUX
 	bool "Support NSA Security Enhanced Linux"
 	default n
+	depends on PLATFORM_LINUX
 	help
 	  Enable support for SELinux in applets ls, ps, and id. Also provide
 	  the option of compiling in SELinux applets.