The build system overlays multiple source trees (repositories) such that
they can shadow libraries and include search paths. This patch extends
the shadowing concept to build targets. Furthermore, it streamlines the
build stage for generating library depenencies, reducing the processing
time of this stage by 10-20 percent. Fixes#165.
In the compare_output_to function in the run tool a check was introduced,
whether the given arguments are empty, and if so if the output string is it
too. Without this patch compare_output_to succeeded when the given pattern
was empty but output wasn't. Please refer to issue #162.
In addition to autogen and autoconf, the tool-chain build script
requires ncurses (for building GDB), wget (to download the tool-chain
source code), and texinfo. Let the tool check if these packages are
installed instead of failing later during the build.