Config: escalate environment not compiling on linux Mint 20

[DraTeots]

I have a fresh linux Mint 20 on a desktop machine (before it was linux mint 19 identified as Ubuntu 18 by spack). While Mint should be fully compatible with ubuntu some package versions could be different. Looks like it has gcc9.3 and escalate environment is configured with kind of manual gcc settings so it doesn't work on this machine. This issue is actually not about linux Mint only, but probably about myriads of other Ubuntu flavours.

Steps to reproduce the issue

$ spack env activate escalate
$ spack concretize 
...
==> Error: SpecList specs refers to named list compilers which does not appear in its reference dict

Information on your system

$ gcc --version
gcc (Ubuntu 9.3.0-17ubuntu1~20.04) 9.3.0

$ uname -a
Linux romanov-bbox 5.4.0-54-generic #60-Ubuntu SMP Fri Nov 6 10:37:59 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux

$ spack debug report
* **Spack:** 0.16.0-29-f613e10f2
* **Python:** 3.8.5
* **Platform:** linux-linuxmint20-zen
* **Concretizer:** original

[wdconinc]

While addressing #80 the environments are now built differently. Let me first fix #80 and then come back to this.

For now, if you want to build the environments yourself, remove the OS and compiler statements at the top.

[wdconinc]

Try with the last updates.

[wdconinc]

I realized that putting all OSes into the environment does prevent it from working on systems without those compilers. Unfortunately, we do need those sections in the environments that are built for cvmfs. I'll figure out how to do that for cvmfs separately than for eic-spack here. But: to be able to use them interchangeably, environments must be a single package with the versions specified as dependencies, the way the most recent commit introduced. In cvmfs, we can only build those environments in a parallel structure for various operating systems by having it this way. Separate packages with concretization together, as before, are not possible unfortunately.