FCVS Fortran 77 Test Suite

FCVS is a freely available Fortran test suite [1]. It is distributed as a compressed tar file.

What's the recommended path for integrating such a suite with llvm-project?

There's no license file in the tar file. However, there's this:

Software Acknowledgment and Redistribution [2]

The conformance test suites provided here are released by the National Institute of Standards and Technology (NIST), an agency of the U.S. Department of Commerce, Gaithersburg MD 20899, USA. The test suites bear no warranty, either express or implied. NIST does not assume legal liability nor responsibility for a User's use of a test suite or the results of such use.

Please note that within the United States, copyright protection, under Section 105 of the United States Code, Title 17, is not available for any work of the United States Government and/or for any works created by United States Government employees. User acknowledges that these test suites contain work which was created by NIST employees and is therefore in the public domain and not subject to copyright. The User may use, distribute, or incorporate these test suites provided the User acknowledges this via an explicit acknowledgment of NIST-related contributions to the User's work. User also agrees to acknowledge, via an explicit acknowledgment, that any modifications or alterations have been made to these test suites before redistribution.

[1] https://www.itl.nist.gov/div897/ctg/fortran_form.htm
[2] https://www.itl.nist.gov/div897/ctg/softagre.htm