Run-time API for compile-time provenance

[jedbrown]

xSDK policy specifies

M8. Each package must provide a runtime API, for example a function call, to return the current
version number of the software and indicate what configure/CMAKE and compiler options were used
to build the package. For development versions of the software, each package must provide the
current commit ID in the repository. With this information users should be able to rebuild the package
in the same state. We do not currently require that version information for all dependent packages be
provided, so it may not be possible to rebuild the entire software stack in the same state.

We provide CeedGetVersion() for release versions, but need to add:

• CeedGetGitVersion() to return the output of git describe (or git rev-parse @). This should also probably indicate whether the build tree is dirty (since then it's not defined by the version, but I don't think we should refuse to build if the tree is dirty).
• CeedGetBuildConfiguration() (name could be different) that reports compiler versions and flags.