UPSTREAM: compiler, clang: suppress warning for unused static inline functions

GCC explicitly does not warn for unused static inline functions for
-Wunused-function.  The manual states:

	Warn whenever a static function is declared but not defined or
	a non-inline static function is unused.

Clang does warn for static inline functions that are unused.

It turns out that suppressing the warnings avoids potentially complex

Suppress the warning for clang.

Signed-off-by: David Rientjes <rientjes@google.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
(cherry picked from commit abb2ea7d)
Signed-off-by: Greg Hackmann <ghackmann@google.com>

Change-Id: I68e6246b03c962cc87b9d0bf4b7fefeda27068c0