* guix/build-system/scons.scm (default-scons): Find "scons" package in (gnu packages python-xyz) instead of (gnu packages python).
* guix/build-system/scons.scm: New file. * guix/build/scons-build-system.scm: New file. * Makefile.am (MODULES): Register them. * doc/guix.texi (Build Systems): Add scons-build-system.