Fix ctrl-c when debugging WOW64 processes

Fix ctrl-c when debugging WOW64 processes

DebugBreakProcess starts a new thread in the target process with the
entry point DbgUiRemoteBreakin, where an int3 triggers a breakpoint
exception for gdb.

But this uses DbgUiRemoteBreakin of the 64bit ntdll.dll even for
WOW64 processes.
It stops in 64bit code, Wow64GetThreadContext reports a wrong pc without
the int3, and gdb lets the target process continue.

So this uses DbgUiRemoteBreakin of the 32bit ntdll.dll as the thread
entry point for WOW64 processes instead.

gdb/ChangeLog:

2020-09-17  Hannes Domani  <ssbssa@yahoo.de>

	* windows-nat.c (ctrl_c_handler): Use 32bit DbgUiRemoteBreakin
	for WOW64 processes.