Bug when building multiple versions of LLVM in one call to easybuild

[Crivella]

Currently building multiple EasyConfigs for LLVM at once will most likely fail due to the global dictionary general_opts being reused

See #3741, in particular

• ensure sysroot dynamic linker is used + add ignore patterns for failing tests that can be ignored in LLVM easyblock #3741 (comment)
• ensure sysroot dynamic linker is used + add ignore patterns for failing tests that can be ignored in LLVM easyblock #3741 (comment)

Fix

Use the global general_opts only for grouping and initialization and work with an internal copy of the dictionary in the class

[Flamefire]

Fixing this in #3755 to allow properly testing it

I see, been wondering about those too. I updated the easyblock PR to handle it: Rename the global constants to uppercase to clearly indicate their nature as constants. Their values are then copied to the instance