After some very confused debugging, I discovered that GNU make has a
main() function with this signature:
int main(int argc, char** argv, char** envp)
Apparently this is a non-standard but widely supported thing, so let's
do the same in Serenity so make works as expected.
This fixes an issue where you had to do "make PATH=..." instead of make
just picking up PATH from the environment. :^)
Now that the kernel supports thread-local storage, we can declare errno
with the __thread keyword, which causes it to be per-thread.
This should fix all the stupid issues that happen when many threads use
the same errno. :^)
