The x86_64 kernel headers are the x86 kernel headers.

Change-Id: I8763aee7043800eb23a720914b57396e79fa812e
diff --git a/libc/kernel/arch-x86_64 b/libc/kernel/arch-x86_64
new file mode 120000
index 0000000..fb7033c
--- /dev/null
+++ b/libc/kernel/arch-x86_64
@@ -0,0 +1 @@
+arch-x86
\ No newline at end of file