i#1987 Win10-1607: update winsysnums to find split usercalls
i#1987 Win10-1607: update winsysnums to find split usercalls

Win10-1607 moves win32k.sys syscall wrappers to a new library,
win32u.dll.  This means that winsysnums -usercalls needs to look at
user32.dll routines invoking imports rather than raw syscalls, with
additional complexity of two of the targets using a "Local_" direct
call that indirectly gets to the import through other stub layers
rather than a direct import.

Review-URL: https://codereview.appspot.com/302590043

AmesianX/dynamorio,AmesianX/dynamorio,AmesianX/dynamorio,AmesianX/dynamorio,AmesianX/dynamorio