integer-wrap: Force full rebuild when .scl file changes

Since the integer wrapping sanitizer's behavior depends on its associated
.scl file, we must force a full rebuild if the file changes. If not,
instrumentation may differ between targets based on when they were built.

Generate a new header file, integer-wrap.h, any time the Clang .scl
file changes. Include the header file in compiler-version.h when its
associated feature name, INTEGER_WRAP, is defined. This will be picked
up by fixdep and force rebuilds where needed.

Acked-by: Justin Stitt <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Reviewed-by: Nicolas Schier <[e-mail]>
Signed-off-by: Kees Cook <[e-mail]>

include/linux/compiler-version.h

···
 #ifdef RANDSTRUCT
 #include <generated/randstruct_hash.h>
 #endif
+
+/*
+ * If any external changes affect Clang's integer wrapping sanitizer
+ * behavior, a full rebuild is needed as the coverage for wrapping types
+ * may have changed, which may impact the expected behaviors that should
+ * not differ between compilation units.
+ */
+#ifdef INTEGER_WRAP
+#include <generated/integer-wrap.h>
+#endif

scripts/Makefile.ubsan

···
 export CFLAGS_UBSAN := $(ubsan-cflags-y)
 
 ubsan-integer-wrap-cflags-$(CONFIG_UBSAN_INTEGER_WRAP)     +=	\
+	-DINTEGER_WRAP						\
 	-fsanitize-undefined-ignore-overflow-pattern=all	\
 	-fsanitize=signed-integer-overflow			\
 	-fsanitize=unsigned-integer-overflow			\

scripts/basic/Makefile

···
 $(obj)/randstruct.seed: $(gen-randstruct-seed) FORCE
 	$(call if_changed,create_randstruct_seed)
 always-$(CONFIG_RANDSTRUCT) += randstruct.seed
+
+# integer-wrap: if the .scl file changes, we need to do a full rebuild.
+$(obj)/../../include/generated/integer-wrap.h: $(srctree)/scripts/integer-wrap-ignore.scl FORCE
+	$(call if_changed,touch)
+always-$(CONFIG_UBSAN_INTEGER_WRAP) += ../../include/generated/integer-wrap.h