kbuild: use -Oz instead of -Os when using clang

BugLink: https://bugs.launchpad.net/bugs/1810958

commit 6748cb3c upstream.

This generates smaller resulting object code when compiled with clang.
Signed-off-by: Behan Webster <behanw@converseincode.com>
Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
[nc: Adjust context due to lack of commit a76bcf55 in linux-4.4.y]
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Juerg Haefliger <juergh@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

Makefile

@@ -644,7 +644,7 @@ KBUILD_CFLAGS	+= $(call cc-disable-warning, int-in-bool-context)
 KBUILD_CFLAGS	+= $(call cc-disable-warning, attribute-alias)
 
 ifdef CONFIG_CC_OPTIMIZE_FOR_SIZE
-KBUILD_CFLAGS	+= -Os
+KBUILD_CFLAGS	+= $(call cc-option,-Oz,-Os)
 else
 ifdef CONFIG_PROFILE_ALL_BRANCHES
 KBUILD_CFLAGS	+= -O2