This lets our system() and popen() commands function sort of like
BusyBox and ToyBox. By default the Cosmopolitan Shell is lightweight.
But if you use STATIC_YOINK then you can pull the individual commands
you want into the linkage, and they'll be included in a single binary.
For example the demo binary embeds `tr` and `sed` and ends up ~140kb.
This program popped up on Hacker News recently. It's the only modern
compiler I've ever seen that doesn't have dependencies and is easily
modified. So I added all of the missing GNU extensions I like to use
which means it might be possible soon to build on non-Linux and have
third party not vendor gcc binaries.
