[WIP] Add script to run each package to detect unbound vars

[springmeyer]

We have some remaining packages with unbound variables that are broken after #356.

This PR is an attempt to detect and fix them.

Currently seeing:

apitrace 6a30de1 /Users/dane/projects/mason/mason.sh: line 297: MASON_LIB_FILE: unbound variable
mesa 11.2.2 /Users/dane/projects/mason/mason.sh: line 297: MASON_LIB_FILE: unbound variable
mesa 13.0.3 /Users/dane/projects/mason/mason.sh: line 297: MASON_LIB_FILE: unbound variable
mesa 13.0.4 /Users/dane/projects/mason/mason.sh: line 297: MASON_LIB_FILE: unbound variable
minjur a2c9dc871369432c7978718834dac487c0591bd6 /Users/dane/projects/mason/mason.sh: line 297: MASON_LIB_FILE: unbound variable
minjur feac70472f46c3145b6bdf7a02fdc37777828318 /Users/dane/projects/mason/mason.sh: line 297: MASON_LIB_FILE: unbound variable
or-tools 5.1 /Users/dane/projects/mason/scripts/or-tools/5.1/script.sh: line 91: DIR: unbound variable