* build: skip default prefix as '/usr'
Distributions that ship this package will always provide the correct
system prefix, sysconfdir, libdir and such.
As a sane default, the package should use the meson default prefix set
to '/usr/local', which is also the standard in many other build
setups (e.g. autotools...).
* build: print actual full paths in meson output
Do not print the option values, print the full built paths.