Simplify (and fix) FindGLib2.cmake
Simplify (and fix) FindGLib2.cmake

When searching for libraries and includes, add `$ENV{GLIB_PATH}` to (a
local copy of) `CMAKE_PREFIX_PATH` rather than specifying the paths
manually. Modify helper to find includes to take an optional list of
libraries to use as additional search paths, which drastically
simplifies how we find glibconfig.h (and may be necessary in case
multiple copies for different architectures are installed).

This also "fixes" (by completely refactoring the relevant logic) a bug
where `CMAKE_LIBRARY_ARCHITECTURE` paths were not being added due to an
egregious typo.

lcm-proj/lcm,adeschamps/lcm,adeschamps/lcm,bluesquall/lcm,bluesquall/lcm,adeschamps/lcm,adeschamps/lcm,adeschamps/lcm,lcm-proj/lcm,bluesquall/lcm,adeschamps/lcm,bluesquall/lcm,bluesquall/lcm,lcm-proj/lcm,bluesquall/lcm,lcm-proj/lcm,lcm-proj/lcm,lcm-proj/lcm,adeschamps/lcm,lcm-proj/lcm,adeschamps/lcm,bluesquall/lcm,lcm-proj/lcm