Permit silencing of __deprecated warnings.

The __deprecated marker is quite useful in highlighting the remnants of
old APIs that want removing.

However, it is quite normal for one or more years to pass, before the
(usually ancient, bitrotten) code in question is either updated or
deleted.

Thus, like __must_check, add a Kconfig option that permits the silencing
of this compiler warning.

This change mimics the ifdef-ery and Kconfig defaults of MUST_CHECK as
closely as possible.

Signed-off-by: Jeff Garzik <jgarzik@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

lib/Kconfig.debug

@@ -9,6 +9,14 @@ config PRINTK_TIME
 	  operations.  This is useful for identifying long delays
 	  in kernel startup.
 
+config ENABLE_WARN_DEPRECATED
+	bool "Enable __deprecated logic"
+	default y
+	help
+	  Enable the __deprecated logic in the kernel build.
+	  Disable this to suppress the "warning: 'foo' is deprecated
+	  (declared at kernel/power/somefile.c:1234)" messages.
+
 config ENABLE_MUST_CHECK
 	bool "Enable __must_check logic"
 	default y