Make libwinpthread a prebuilt_cc_library_static am: a6fee370be am: e1994880d0 am: 8c55508f87

Original change: https://android-review.googlesource.com/c/platform/prebuilts/gcc/linux-x86/host/x86_64-w64-mingw32-4.8/+/1950276

Change-Id: Ieecb26c41dbea9920bb5bfe692740db00b27d476