Update to v5.6 kernel headers.

Kernel headers coming from:

Git: https://android.googlesource.com/kernel/common/
Branch: android-mainline
Tag: android-mainline-5.6

Add a new method for removing structures. This is to deal with the kernel
headers changing some definitions of timeval to __kernel_old_timeval
and itimerval to __kernel_old_itimerval. Remove the __kernel_old_XX
strutures and change the other structures to the previous definitions.

This only works so long as these structures stay the same, if they
diverge, then a different strategy will need to be implemented.

Test: Booted cuttlefish/walleye.
Test: Ran bionic-unit-tests on cuttlefish/walleye.
Change-Id: I0a61f4fa6e4155c602e0414d9b38c2e1637829af
diff --git a/libc/kernel/uapi/asm-generic/unistd.h b/libc/kernel/uapi/asm-generic/unistd.h
index 2128ff5..1b85b30 100644
--- a/libc/kernel/uapi/asm-generic/unistd.h
+++ b/libc/kernel/uapi/asm-generic/unistd.h
@@ -396,8 +396,10 @@
 #ifdef __ARCH_WANT_SYS_CLONE3
 #define __NR_clone3 435
 #endif
+#define __NR_openat2 437
+#define __NR_pidfd_getfd 438
 #undef __NR_syscalls
-#define __NR_syscalls 436
+#define __NR_syscalls 439
 #if __BITS_PER_LONG == 64 && !defined(__SYSCALL_COMPAT)
 #define __NR_fcntl __NR3264_fcntl
 #define __NR_statfs __NR3264_statfs