kasan: always respect CONFIG_KASAN_STACK

Currently, the asan-stack parameter is only passed along if
CFLAGS_KASAN_SHADOW is not empty, which requires KASAN_SHADOW_OFFSET to
be defined in Kconfig so that the value can be checked.  In RISC-V's
case, KASAN_SHADOW_OFFSET is not defined in Kconfig, which means that
asan-stack does not get disabled with clang even when CONFIG_KASAN_STACK
is disabled, resulting in large stack warnings with allmodconfig:

  drivers/video/fbdev/omap2/omapfb/displays/panel-lgphilips-lb035q02.c:117:12: error: stack frame size (14400) exceeds limit (2048) in function 'lb035q02_connect' [-Werror,-Wframe-larger-than]
  static int lb035q02_connect(struct omap_dss_device *dssdev)
             ^
  1 error generated.

Ensure that the value of CONFIG_KASAN_STACK is always passed along to
the compiler so that these warnings do not happen when
CONFIG_KASAN_STACK is disabled.

Link: ClangBuiltLinux#1453
References: 6baec88 ("kasan: turn off asan-stack for clang-8 and earlier")
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Nathan Chancellor <[email protected]>
Reviewed-by: Marco Elver <[email protected]>
Cc: Andrey Ryabinin <[email protected]>
Cc: Alexander Potapenko <[email protected]>
Cc: Andrey Konovalov <[email protected]>
Cc: Dmitry Vyukov <[email protected]>
Cc: Nick Desaulniers <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

scripts/Makefile.kasan

@@ -33,10 +33,11 @@ else
 	CFLAGS_KASAN := $(CFLAGS_KASAN_SHADOW) \
 	 $(call cc-param,asan-globals=1) \
 	 $(call cc-param,asan-instrumentation-with-call-threshold=$(call_threshold)) \
-	 $(call cc-param,asan-stack=$(stack_enable)) \
 	 $(call cc-param,asan-instrument-allocas=1)
 endif
 
+CFLAGS_KASAN += $(call cc-param,asan-stack=$(stack_enable))
+
 endif # CONFIG_KASAN_GENERIC
 
 ifdef CONFIG_KASAN_SW_TAGS