Pitfall: environment variables

[awdeorio]

Environment variables like CXX and CXXFLAGS can cause problems with the VS Code tutorial. Add Troubleshooting subsection to check for them.

A specific example that I've seen is CXXFLAGS=-O2 ... set by some Anaconda-like (can't remember the name) Python install from source. When the student used our Makefile, the environment-provided CXXFLAGS compiled with optimization and without -g. When the student completed the lab2 debugging tutorial, they got dumped into ASM code instead of a nice "stop on the line where the program failed". TAs had trouble figuring this one out.

[hardy-ethan]

polluting the global (within the environment) CXXFLAGS is crazy work 😭