Generate .pc and .cmake files during install.

[brettviren]

Eg, like this:

https://groups.google.com/forum/#!topic/waf-users/8uS3ty0z0ik

[drbenmorgan]

(Just a couple of quick notes from the discussion on the LArSoft list, apologies if these are obvious/known!) For the .pc file, to help in relocatability, the ${pcfiledir} directive/variable can be used to self-locate the .pcfile and derive paths from it, e.g

prefix=${pcfiledir}/../..
incdir=${prefix}/include
...

I'd guess the relative path from the pkg-config install location to install prefix and similar can be derived easily in the waf scripts and turned into expansion variables.

For the .cmake files, and again to help in relocatability, the new imported targets with usage requirements can be used: https://cmake.org/cmake/help/v3.5/manual/cmake-buildsystem.7.html.
These are fully relocatable, make usage easier as required flags like `-I' are added automatically, and handle transitive dependencies (fairly) easily.