Support MD5 with a warning when OpenSSL is compiled in FIPS mode (#7531)
Support MD5 with a warning when OpenSSL is compiled in FIPS mode (#7531)

* This allows Spack to work with MD5 hashes on machines with openssl in FIPS mode.
* We are still using MD5 for validation in many places, and a later PR will replace all uses of MD5 with SHA256.
* This is a quick fix until that happens.
LLNL/spack,iulian787/spack,LLNL/spack,LLNL/spack,krafczyk/spack,EmreAtes/spack,mfherbst/spack,mfherbst/spack,iulian787/spack,matthiasdiener/spack,EmreAtes/spack,iulian787/spack,tmerrick1/spack,tmerrick1/spack,matthiasdiener/spack,tmerrick1/spack,krafczyk/spack,EmreAtes/spack,matthiasdiener/spack,EmreAtes/spack,LLNL/spack,mfherbst/spack,matthiasdiener/spack,EmreAtes/spack,krafczyk/spack,matthiasdiener/spack,mfherbst/spack,iulian787/spack,krafczyk/spack,LLNL/spack,tmerrick1/spack,krafczyk/spack,iulian787/spack,mfherbst/spack,tmerrick1/spack