commandline: support more library specifications when linking tools

Change-Id: Ib9b72602873ebd1f62a3165555852b949c79afb8
protobuf: support an external protobuf

We need to masquerade protobuf_compiler with the actual protobuf
executable from outside the system.

Change-Id: Ibb4db838e5422fcfaf1cad2a9edb2d73a77e9b24
pugixml: add a module to find pugixml installs

Change-Id: I046029361bb4d1cdf91bda8eb4761812b2d539e3
Merge topic 'use-system-libraries' into next

fc62b085 pugixml: add a module to find pugixml installs
b1d98fb9 protobuf: support an external protobuf
9cfa6867 commandline: support more library specifications when linking tools