Update to easyblocks to add lfoss toolchain support [SCOTCH/MUMPS]

[hattom]

SCOTCH's Easyblock had two sections which explicitly depended on the toolchain:
The first was for the name of the Makefile:

if intel:
 ...
elif GCC:
 ...
else:
 raise ...

The other was for the restrict keyword:

if GCC:
  ...
else
  ...

For both cases, add LLVM to the GCC behaviour, and modify the syntax to match in both cases (compiler order, raise if else, define a comp_fam variable)

[hattom]

A generalization to support also NVHPC is left as a future exercise, but would presumably follow exactly the same pattern.

[hattom]

btw -- I'm working my way through to get PETSc building. These are the problems that I've found so far, but I'm not finished yet (building python etc is taking a very long time).