build: fix Makefile wrt finding node executable

Not all shells set PWD, so use CURDIR instead.

`which node` may return the empty string, so guard against
that too. Consider:
if [ -x `which velociraptor` ] && [ -e `which velociprator` ];\
then echo "run"; else echo "keep calm"; fi;

PR-URL: https://github.com/nodejs/node/pull/18040


Reviewed-By: Evan Lucas <evanlucas@me.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>