Enforce custom rpmbuild build dir

[schrnz]

The following error is generated for
make rpm

$ make rpm
mkdir -p rpmbuild/SOURCES/artist-sdk-0.0.1
cd src && cp -r include toolchain makefiles LICENSE Makefile ../rpmbuild/SOURCES/artist-sdk-0.0.1/
cd rpmbuild/SOURCES && tar -zcf artist-sdk-0.0.1.tar.gz artist-sdk-0.0.1 && rm -r artist-sdk-0.0.1
rpmbuild -bb rpmbuild/SPECS/artist-sdk.spec
error: File /home/<username>/rpmbuild/SOURCES/artist-sdk-0.0.1.tar.gz: No such file or directory

It seems rpmbuild is by default assuming that the rpmbuild working dir is the home folder. In theory it should be possible to change this locally (blog entry), but the proposed fix did not work when I tried it.

Symlinking ~/rmpbuild to point to module-sdk-gen/rpmbuild is a workaround that works for now, so the issue is low priority, but it would still be nice to have this solved in the Makescript itself.