kasan: remove clang version check for KASAN_STACK

asan-stack mode still uses dangerously large kernel stacks of tens of
kilobytes in some drivers, and it does not seem that anyone is working
on the clang bug.

Turn it off for all clang versions to prevent users from accidentally
enabling it once they update to clang-9, and to help automated build
testing with clang-9.

Link: https://bugs.llvm.org/show_bug.cgi?id=38809
Link: http://lkml.kernel.org/r/20190719200347.2596375-1-arnd@arndb.de
Fixes: 6baec880 ("kasan: turn off asan-stack for clang-8 and earlier")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Mark Brown <broonie@kernel.org>
Reviewed-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Qian Cai <cai@lca.pw>
Cc: Andrey Konovalov <andreyknvl@google.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

lib/Kconfig.kasan

@@ -106,7 +106,6 @@ endchoice
 
 config KASAN_STACK_ENABLE
 	bool "Enable stack instrumentation (unsafe)" if CC_IS_CLANG && !COMPILE_TEST
-	default !(CLANG_VERSION < 90000)
 	depends on KASAN
 	help
 	  The LLVM stack address sanitizer has a know problem that
@@ -115,11 +114,11 @@ config KASAN_STACK_ENABLE
 	  Disabling asan-stack makes it safe to run kernels build
 	  with clang-8 with KASAN enabled, though it loses some of
 	  the functionality.
-	  This feature is always disabled when compile-testing with clang-8
-	  or earlier to avoid cluttering the output in stack overflow
-	  warnings, but clang-8 users can still enable it for builds without
-	  CONFIG_COMPILE_TEST.  On gcc and later clang versions it is
-	  assumed to always be safe to use and enabled by default.
+	  This feature is always disabled when compile-testing with clang
+	  to avoid cluttering the output in stack overflow warnings,
+	  but clang users can still enable it for builds without
+	  CONFIG_COMPILE_TEST.	On gcc it is assumed to always be safe
+	  to use and enabled by default.
 
 config KASAN_STACK
 	int