CHROMIUM: kbuild: clang: Disable the 'duplicate-decl-specifier' warning

clang generates plenty of these warnings in different parts of the code.
They are mostly caused by container_of() and other macros which declare
a "const <type> *" variable for their internal use which triggers a
"duplicate 'const' specifier" warning if the <type> is already const
qualified.

Change-Id: I3ad9d33e31b7b40f926554eed2afeea1ebb7e961
Wording-mostly-from: Michael Davidson <md@google.com>
Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
diff --git a/Makefile b/Makefile
index 9fab6a0..d01f266 100644
--- a/Makefile
+++ b/Makefile
@@ -714,6 +714,7 @@
 KBUILD_CFLAGS += $(call cc-disable-warning, format-invalid-specifier)
 KBUILD_CFLAGS += $(call cc-disable-warning, gnu)
 KBUILD_CFLAGS += $(call cc-disable-warning, address-of-packed-member)
+KBUILD_CFLAGS += $(call cc-disable-warning, duplicate-decl-specifier)
 # Quiet clang warning: comparison of unsigned expression < 0 is always false
 KBUILD_CFLAGS += $(call cc-disable-warning, tautological-compare)
 # CLANG uses a _MergedGlobals as optimization, but this breaks modpost, as the