#2410: compiling Baikal with gcc >= 9.3 is very slow

It was found that is it slow compile of Baikal code with gcc 9.3.0 or newer (10.1 is also affected)

takes about 30 minutes to compile 8th order FD RHS using gcc 9.3.0 using -O1 and -march=core2
Zach and Roland have been looking into this
slowness goes away if one uses gcc -Q -O1 --help=optimizers which claims to report the options that are used by -O1

Zach wanted to look into moving operators into non-inlined files anyway which may fix the issue.