OpenSSL3 deprecates MD5

[rgmiller]

System information

Type	Version/Name
Operating System	Ubuntu
OS Version	22.04
Architecture	x86_64
UnifyFS Version	Latest from Git

Describe the problem you're observing

When attempting to build UnifyFS on an Ubuntu 22.04 system, gcc prints a warning saying that the MD5 function has been deprecated. Since we compile with -Werror, this warning halts the build.

The warning stems from the OpenSSL 3 library that is now standard on Unbuntu 22.04.

Describe how to reproduce the problem

Attempt to build on any system that's upgraded to OpenSSL 3.x. (Ubuntu 22.04 is a good example.)

Include any warning or errors or releveant debugging data

Replacing the call to MD5 (unifyfs_meta.c) with calls to OpenSSL EVP_Digest* functions should be pretty straight-forward. These functions exist at least as far back as the OpenSSL versions in RHEL7, so there shouldn't be any problem with builds on older systems.