Add the common directory back to kernel headers.

This is a port of build/ change 6a2f28514.

Change-Id: I9128abf61a56e282f335f540fcf064dd52706b2b
diff --git a/cc/arm64_device.go b/cc/arm64_device.go
index dcdce0f..4e41287 100644
--- a/cc/arm64_device.go
+++ b/cc/arm64_device.go
@@ -103,6 +103,7 @@
 		"-isystem ${LibcRoot}/arch-arm64/include",
 		"-isystem ${LibcRoot}/include",
 		"-isystem ${LibcRoot}/kernel/uapi",
+		"-isystem ${LibcRoot}/kernel/common",
 		"-isystem ${LibcRoot}/kernel/uapi/asm-arm64",
 	}, " "))