HostThreadPosix::Cancel: remove android-specific implementation
HostThreadPosix::Cancel: remove android-specific implementation

Noone is calling this function on android, so we can just use the
generic llvm_unreachable "implementation".

git-svn-id: 4c4cc70b1ef44ba2b7963015e681894188cea27e@326777 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/lldb,llvm-mirror/lldb,apple/swift-lldb,apple/swift-lldb,apple/swift-lldb,llvm-mirror/lldb,apple/swift-lldb,llvm-mirror/lldb,llvm-mirror/lldb,apple/swift-lldb,apple/swift-lldb