No color for compiler errors

[MakisH]

I have noticed that OpenFOAM overrides the default behavior of GCC to annotate errors, warnings, etc. This makes it pretty tiring sometimes to read compiler messages.

Defining ADAPTER_PREP_FLAGS="-fdiagnostics-color=always" in Allwmake seems to help, but probably there is a better way to set this. I opened an upstream issue.