Use the new functionality for new project specific array variables:
- CONFIGURE_VARS: elements of the form NAME=VALUE will be set as
environment variables when running autoconfig configure.
- CONFIGURE_OPTS: elements will be added to the options passed to
autoconfig configure.
* Use common prefixes for project specific build step functions:
- ossbuild-prepare-<prjname>
- ossbuild-build-<prjname>
- ossbuild-install-<prjname>
* New project specific build step function: ossbuild-configure-ok-p-<prjname>
* New environment variable OSSBUILD_SKIP. Allows users to skip listed
(comma separated) build steps.
* Remove `-generic` from common function names.
* Improve ossbuild-pushd/popd functions.
* Improve doc comments.
* Adapt projects to renamed functions
