Compilation fixes

[bjourne]

A few little compiler warnings cleanups and makefile improvements. I also think you should consider changing -O2 to -O3 as that makes the c_fast benchmark much faster when compiled with clang. Clang in general beats gcc on my machine.

[lgeek]

-march=native is not equivalent to -mcpu=native. It needs to be -march=native -mtune=native.

[bjourne]

-march implies -mtune, see https://gcc.gnu.org/onlinedocs/gcc-4.3.2/gcc/i386-and-x86_002d64-Options.html

[lgeek]

It's not documented to work like that in the GCC ARM docs. Also, the options accepted by -march are generic architectures, while the options accepted by -mtune are specific cores.

[bjourne]

But previously the makefile didn't even specify -mtune. -march at least implies -mcpu.

[bjourne]

@lgeek, I apologise for not making myself more clear. My intention with this pr was not to invest to much time in your LPathBench project. I just wanted to share the changes I needed to make it work well for me. Feel free to reject this pr, apply it or do whatever you want with it. Sorry, but I don't have either the time or the interest in working more on it.

[lgeek]

@bjourne Sorry if this is wasn't clear, but this is not my project. I just wrote the c-fast implementation and I've only reviewed the patches related to it. It's not up to me what gets merged. I've pointed out the changes which either break things (e.g. the printf one) or which change behavior (the flags).

[bjourne]

I think "%"PRIu64 is the right way to express the format. Though it appears that %lu does not break anything on 32bit platforms.