i#4075: Fix deadlock on double takeover

[derekbruening]

Fixes a double-takeover deadlock by changing
nt_wait_event_with_timeout() to use a raw syscall to keep the PC in
dynamorio.dll for os_take_over_all_unknown_threads() (and synch_with_*
and other routines) to more easily identify a thread in DR code. In
particular this is required to avoid a double takeover on a race
between intercept_new_thread() and os_take_over_all_unknown_threads().

Fixes #4075

[derekbruening]

AArch64 is #3980. Appveyor is another for #4058, but all of the test failures by timeout are gone, so this seems to have fixed those as well. nudge_test is passing but with #4077 maybe it shouldn't be de-flaked just yet.