The Nim compiler knows nothing about CFLAGS and related things, however the C
compiler it uses should (if you're using GCC or Clang). You can also pass in
arguments via `--passC` and `--passL` arguments.
When benchmarking, it's good to remember some things:
* Nim's `int` datatype is always the size of the target architecture's
pointer type (32 bits on x86, 64 on x86-64). This can cause disparities in
benchmarks.
* Putting main code in the global scope of a module prevents certain
optimizations. When aiming for optimization, put things in a main procedure.
* Profile guided optimization and link time optimization can work really well
with regards to speed. Link time optimization also tends to have a significant
effect on executable size too.
* Depending on how fair you want to be, you can turn off the mark and sweep
portion of the garbage collector if you're sure the benchmark doesn't generate
any reference cycles. The regular reference counting garbage collector will
still run.
