c++: module mapper

To avoid always requiring an active mapper to connect to, we provide a
default in-process mapper with similar functionality to the sample
server.  This is that code.  Also included is the client-side
connection mechanism, which determines what server to use and how to
connect to it.

	gcc/cp/
	* Make-lang.in (CXX_AND_OBJCXX_OBJS): Add mapper-client &
	mapper-resolver.
	* mapper-client.h: New.
	* mapper-client.cc: New.
	* mapper-resolver.cc: New.