Update to v4.15 kernel headers.

Test: Compiles, boots bullhead/hikey960.
Change-Id: I118beb8b6cac0881b1270f9bf6981959297a41a8
diff --git a/libc/kernel/uapi/linux/input-event-codes.h b/libc/kernel/uapi/linux/input-event-codes.h
index 346ec91..da90f1c 100644
--- a/libc/kernel/uapi/linux/input-event-codes.h
+++ b/libc/kernel/uapi/linux/input-event-codes.h
@@ -359,6 +359,7 @@
 #define BTN_TOOL_MOUSE 0x146
 #define BTN_TOOL_LENS 0x147
 #define BTN_TOOL_QUINTTAP 0x148
+#define BTN_STYLUS3 0x149
 #define BTN_TOUCH 0x14a
 #define BTN_STYLUS 0x14b
 #define BTN_STYLUS2 0x14c