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/coreutils/Config.src b/coreutils/Config.src
index d4c9e05..780b73f 100644
--- a/coreutils/Config.src
+++ b/coreutils/Config.src
@@ -591,6 +591,7 @@
 config STAT
 	bool "stat"
 	default y
+	depends on PLATFORM_LINUX # statfs()
 	help
 	  display file or filesystem status.
 
@@ -606,6 +607,7 @@
 config STTY
 	bool "stty"
 	default y
+	depends on PLATFORM_LINUX
 	help
 	  stty is used to change and print terminal line settings.
 
diff --git a/coreutils/date.c b/coreutils/date.c
index c737f09..cb41724 100644
--- a/coreutils/date.c
+++ b/coreutils/date.c
@@ -72,7 +72,7 @@
 //config:config FEATURE_DATE_NANO
 //config:	bool "Support %[num]N nanosecond format specifier"
 //config:	default n
-//config:	depends on DATE
+//config:	depends on DATE && PLATFORM_LINUX # syscall(__NR_clock_gettime)
 //config:	help
 //config:	  Support %[num]N format specifier. Adds ~250 bytes of code.
 //config: