Import afunix.h from MinGW am: 13b39ee0bc

Original change: https://android-review.googlesource.com/c/platform/prebuilts/gcc/linux-x86/host/x86_64-w64-mingw32-4.8/+/2952707

Change-Id: I6a65b1ea5f6473517ac0971d9090c447788fbd04
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>