Add linux/userfaultfd.h header file to host glibc am: 9993489d1c

Original change: https://android-review.googlesource.com/c/platform/prebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.17-4.8/+/1999534

Change-Id: Ie5d1af79ff70f9eba3e1b4d67286def30114ed9c