Revert "BACKPORT: kasan: remove redundant config option"

This reverts commit 13aefe4bf8.

That commit might lead to stack overflows with x86 KASAN with stack
instrumentation enabled and has been dropped from the mm tree.
Revert the change for now.

Bug: 172318110
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Change-Id: I5020ec2361d5f9976d0666e0c1ed6925e29fa5b2

scripts/Makefile.kasan

@@ -2,12 +2,6 @@
 CFLAGS_KASAN_NOSANITIZE := -fno-builtin
 KASAN_SHADOW_OFFSET ?= $(CONFIG_KASAN_SHADOW_OFFSET)
 
-ifdef CONFIG_KASAN_STACK
-	stack_enable := 1
-else
-	stack_enable := 0
-endif
-
 ifdef CONFIG_KASAN_GENERIC
 
 ifdef CONFIG_KASAN_INLINE
@@ -33,7 +27,7 @@ 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)) \
+	 $(call cc-param,asan-stack=$(CONFIG_KASAN_STACK)) \
 	 $(call cc-param,asan-instrument-allocas=1)
 endif
 
@@ -48,7 +42,7 @@ else
 endif
 
 CFLAGS_KASAN := -fsanitize=kernel-hwaddress \
-		-mllvm -hwasan-instrument-stack=$(stack_enable) \
+		-mllvm -hwasan-instrument-stack=$(CONFIG_KASAN_STACK) \
 		-mllvm -hwasan-use-short-granules=0 \
 		$(instrumentation_flags)