Add define for MAKE variable
Currently there is no define for MAKE. Running script always throws `obsolete make version; need GNU make 4.x or later` error.
This config is from [`build-util.sh` script](https://github.com/ucb-bar/chipyard/blob/9d055fdac638ab90735cbde42fd2d86355eb260b/scripts/build-util.sh#L17-L19)
@@ -11,6 +11,10 @@ set -o pipefail
DIR="$(dirname "$(readlink -f "${BASH_SOURCE[0]:-${(%):-%x}}")")"
CHIPYARD_DIR="$(dirname "$DIR")"
+# Allow user to override MAKE
+[ -n "${MAKE:+x}" ] || MAKE=$(command -v gnumake || command -v gmake || command -v make)
+readonly MAKE
+
usage() {
echo "usage: ${0} [OPTIONS] [riscv-tools | esp-tools | ec2fast]"
echo ""
