QB64 should be able to compile programs with -O2

[mkilgore]

Currently QB64 does not compile programs with any optimizations enabled. -O2 is reasonably safe to use and things appear to work (though more testing could be done), but the biggest issue appears to be speed and memory usage: Compiling qb64.bas with -O2 results in a ~15 minute compile on my machine and at one point uses ~10GB of memory, which is completely out of the realm of reasonable.

It appears most things compile fairly snappy (as you would expect) and the big culprit is qbx.cpp which imports main.txt, which is 200 thousand lines long for qb64.bas. Being that this contains all the function definitions in addition to the actual main code, with a lot of work it seems likely that this can be split into several .cpp files that can then get compiled own their own and linked together, significantly reducing the amount of code each gcc process has to deal with.