adb: win32: fix Ctrl-C of adb server nodaemon

On Windows, when running adb server nodaemon and pressing Ctrl-C,
adb_server_cleanup (an atexit handler) would call kick_all_transports()
which would eventually fail a CHECK because the current thread was not
equal to the main thread. This is because Ctrl-C is implemented in
Windows by the OS creating a new thread in the process and calling the
Ctrl-C handler from there.

The CHECK fail would print out the CHECK expression and call abort()
which would record a crash in the Windows Event Log, plus would
potentially upload a crashdump to Microsoft's Watson service.

This might be a regression from d51c6df1.

The fix is to share more code between platforms, removing the call to
Win32 SetConsoleCtrlHandler() and just use the C Runtime's signal()
implementation which is built upon SetConsoleCtrlHandler(). The signal
handler still ends up being called from another thread, but the handler
is thread-safe enough so this seems to work.

Test: On Win10 and Vista, run adb server nodaemon and then try Ctrl-C,
Ctrl-Break and close console window.

Change-Id: I6603970616098d2b3ce68f2a3d4e5515ec859811
Signed-off-by: Spencer Low <CompareAndSwap@gmail.com>