Remove EPICS modules that do not have a dynamic library linked to any
executables in the target IOC. This shrinks the final image size by
removing useless artifacts. We introduce to REPONAME the semantics of
specifying the path where relevant binaries are, when no-build target is
used, so that the proper clean-up can happen in such cases as well.
Previously, REPONAME was not used at all.

The clean up phase must be executed in the build stage (before the final
copy), otherwise the COPY layer would still make the image size big.
This implies `no-build` target needs to copy from a pruned version of
the base image, which is a new stage.

The list of modules to be removed is taken from the RELEASE file, so
that it contains a valid mapping of all modules that have been
installed. EPICS base is assumed to be always needed, even though some
binaries in it can certainly be thrown away given the linkage of the IOC
(for instance, PVAccess binaries when the IOC uses only Channel Access).

Linkage information is taken from ldd(1), which assumes the inspected
binaries are safe to be potentially executed. It is assumed we are using
glibc implementation, which provides a straightforward way to query all
binaries at once.

Static libraries are not used neither during compile time nor runtime
for non-static builds. On the other hand, they take up a large amount of
storage: about 312MB for EPICS base and 222MB for modules.

Remove them all right before finishing the build stages, avoiding their
copy to IOC images.

All AR archives are assumed to be static libraries, which should be a
good assumption in GNU/Linux. Other static artifacts, such as object
files, are correctly removed by the build system clean target and are
not handled explictly here for simplification. A lint script for the
build system can be implemented in the future if this eventually becomes
false.

Shared libraries may be installed either in /opt or /usr/local/lib but
may not be used by the target binaries from the IOC image. Remove them
during the prune phase before copying both directories to resulting
image to shrink the final image size.

Both actual versioned binary and its symbolic links are removed to keep
the filesystem consistent.

Modules may contain several artifacts, including configuration files,
graphical interface files and other repository artifacts that do not
need to be in the IOC image.

Remove them all except the ones containing EPICS database (`.db` and
`.template`) or autosave requirement (`.req`) files, besides shared
libraries. Binaries directory (`bin`) is also removed, as only $REPONAME
and $RUNDIR should contain target executables, which are filtered out
from the list.

EPICS base has rather large configuration files for build, and other
repository files, which are not needed in the IOC images. Prune them
after building the IOCs, shrinking about 40MB the final image size.

Prune is performed with the same script as modules, which discards all
executables in `bin` (~15MB), as well as Perl scripts. This should be
fine considering that `static-link` target also does not preserve EPICS
binaries in the resulting image.