How to change number of threads used in Homebrew builds?
This is what I ended up using:

$ HOMEBREW_MAKE_JOBS=1 HOMEBREW_VERBOSE=1 brew install caskformula/caskformula/inkscape


HOMEBREW_MAKE_JOBS is the number of threads that wold be used in the build process by make and HOMEBREW_VERBOSE is set to one to turn on verbose mode for all tasks performed by Homebrew.