Several install_deps issues

Please fix these issues:

The command line for building blender that install_deps is creating contains the wrong python version 3.7 (here on manjaro, 3.8 is standard):


Every time I run install_deps, I have to correct this manually. Can it be fixed?

It seems as if OpenXR and Alembic are downloaded, unpacked and compiled every time is run (just today it happened five times in a row)

Building Alembic-1.7.12

Connecting to (||:443… connected.

Unpacking Alembic-1.7.12

make -f CMakeFiles/Makefile2 all