title: pythonnet (2.5.2) build failures, offline install
body: <p>VERY new at this, but I've tried almost every site and read almost any documentation I can find.  Our tricky situation is trying to create a system that ultimately supports pythonnet(2.5.2) on a CentOS 7 that has no access to the internet.  We have downloaded and brought a ton of repos and packages to the machine, but keep running into this failure.</p>
  <p>Currently:
  OS: CentOS 7 (stable)
  Python: 3.8.10 (with pycparser 2.21)
  Mono: 6.12.0-107
  Clang: At least 3.4.1, may be 3.4.2
  Dotnet: None, neither runtime nor sdk</p>
  <p>Mono-complete was used for the installation from a locally held, current repo, but we run into one of two issues when trying to install pythonnet.</p>
  <p>In the working directory:
  $ pip3 install pythonnet-2.5.2.tar.gz</p>
  <p>It will start to build the wheel and then it will squawk about legacy-install-failure and will also fail when the system tries to run the subprocess 'mono tools/nuget/nuget.exe --update self'</p>
  <p>Any and all insight would help.  I'm sorry if this is a little sparse on details.  I feel like there is an issue with the mono environment, if not we need to bring in the dotnet-runtime-6.0 or dotnet-sdk-6.0 and try again.  Thanks so much!</p>