adb: fix shell_service_protocol_test for Windows.

Adds missing #ifdef guards to shell_service_protocol_test.cpp so the
test compiles on Windows.

Also fixes a bug in Windows socketpair write implementation. Previously
it was only checking for a closed pipe if the write happened to block.
This adds an additional pre-check to exit immediately on a closed pipe.

These two changes allow the test to compile and pass on Windows.

Change-Id: Ib8853ed72f015fc0d623da47c32982cb3ffa4a3d