Update to v4.17.3 kernel headers.

Test: Builds, boots on a walleye.
Change-Id: I389d8b61ec00ea309e38d1b1a2e0dace48c21edb
diff --git a/libc/kernel/uapi/linux/prctl.h b/libc/kernel/uapi/linux/prctl.h
index 55098f5..ba50b14 100644
--- a/libc/kernel/uapi/linux/prctl.h
+++ b/libc/kernel/uapi/linux/prctl.h
@@ -134,4 +134,12 @@
 #define PR_SVE_GET_VL 51
 #define PR_SVE_VL_LEN_MASK 0xffff
 #define PR_SVE_VL_INHERIT (1 << 17)
+#define PR_GET_SPECULATION_CTRL 52
+#define PR_SET_SPECULATION_CTRL 53
+#define PR_SPEC_STORE_BYPASS 0
+#define PR_SPEC_NOT_AFFECTED 0
+#define PR_SPEC_PRCTL (1UL << 0)
+#define PR_SPEC_ENABLE (1UL << 1)
+#define PR_SPEC_DISABLE (1UL << 2)
+#define PR_SPEC_FORCE_DISABLE (1UL << 3)
 #endif