Update to v4.17.3 kernel headers.

Test: Builds, boots on a walleye.
Change-Id: I389d8b61ec00ea309e38d1b1a2e0dace48c21edb
diff --git a/libc/kernel/uapi/linux/ptrace.h b/libc/kernel/uapi/linux/ptrace.h
index 7c39b5b..4a68738 100644
--- a/libc/kernel/uapi/linux/ptrace.h
+++ b/libc/kernel/uapi/linux/ptrace.h
@@ -50,6 +50,11 @@
 #define PTRACE_GETSIGMASK 0x420a
 #define PTRACE_SETSIGMASK 0x420b
 #define PTRACE_SECCOMP_GET_FILTER 0x420c
+#define PTRACE_SECCOMP_GET_METADATA 0x420d
+struct seccomp_metadata {
+  __u64 filter_off;
+  __u64 flags;
+};
 #define PTRACE_PEEKSIGINFO_SHARED (1 << 0)
 #define PTRACE_EVENT_FORK 1
 #define PTRACE_EVENT_VFORK 2