devel/bazel: update to 0.5.0

Changes: https://github.com/bazelbuild/bazel/releases/tag/0.5.0

While there, also set SOURCE_DATE_EPOCH for the build, unless set already, to
the timestamp in distinfo, to obtain a reproducible binary with a meaningful
timestamp.

PR: 219575
Submitted by: Klaus Aehlig <aehlig@linta.de> (maintainer)