Use common lib.json to build libacpi

Seems like it wasn't used because couldn't build libacpi with -wunused.
lib.json doens't specify this, and we need some other flags to build with gcc, so let's add it back.

Signed-off-by: Graham MacDonald <grahamamacdonald@gmail.com>

sys/src/libacpi/acpica/acpiflags.json

@@ -32,9 +32,6 @@
 			"/sys/include/acpi/acpica"
 		],
 		"Include": [
-			"/$ARCH/$CC.json"
-		],
-		"IncludeCanNotUsedWUnusedYet": [
 			"../../lib.json"
 		],
 		"NoCflags": [