objtool: Set minimum xxhash version to 0.8

XXH3 is only supported starting with xxhash 0.8. Enforce that.

Fixes: 0d83da43b1e1 ("objtool/klp: Add --checksum option to generate per-function checksums")
Closes: https://lore.kernel.org/[e-mail]
Reported-by: Michael Kelley <[e-mail]>
Signed-off-by: Josh Poimboeuf <[e-mail]>
Signed-off-by: Peter Zijlstra (Intel) <[e-mail]>
Reviewed-by: Michael Kelley <[e-mail]>
Tested-by: Michael Kelley <[e-mail]>
Link: https://patch.msgid.link/[e-mail]

tools/objtool/Makefile

···
 endif
 
 ifeq ($(ARCH_HAS_KLP),y)
-	HAVE_XXHASH = $(shell echo "int main() {}" | \
+	HAVE_XXHASH = $(shell printf "$(pound)include <xxhash.h>\nXXH3_state_t *state;int main() {}" | \
 		      $(HOSTCC) -xc - -o /dev/null -lxxhash 2> /dev/null && echo y || echo n)
 	ifeq ($(HAVE_XXHASH),y)
 		BUILD_KLP	 := y

tools/objtool/builtin-check.c

···
 
 #ifndef BUILD_KLP
 	if (opts.checksum) {
-		ERROR("--checksum not supported; install xxhash-devel/libxxhash-dev and recompile");
+		ERROR("--checksum not supported; install xxhash-devel/libxxhash-dev (version >= 0.8) and recompile");
 		return false;
 	}
 #endif