gsl: enable avx-optimized compilation

[NicosPavlov]

The latest apple's clang support now avx instructions, so that it should be now possible to compile GSL with avx optimisations. The attached patch should enable avx instructions in case of the optimize variant if a proper compiler is chosen.

[daitakahashi]

Thank you very much nicos. This is just my preference, but I would like to add another compiler variant, namely mpclang33, rather than implicitly introducing a dependence on the macports' clang-3.3.

Here, I attach my diff, so could you please give me any comments if you like.

[daitakahashi]

add a new variant mpclang33, and modify the optimize variant for consistency

[NicosPavlov]

Sure, I did not include an additional variant because there was not any for clang, but it is indeed definitively better.

One thing is that a gcc48 variant has been recently added, which should probably be added if the conditional.

Another thing, which I wanted to propose to include, although it was not greatly written, was the default case, for which no flags are set for now. In particular, the latest apple clang (>= 5.0) also can handle avx instructions.

I include a new diff which contains these changes, along with your previous modifications. The conditionals could probably be simplified, but the point is to see if you find these changes sensible.

[NicosPavlov]

Add cflags also for default compiler

[daitakahashi]

I removed an XCode-version check, because the assembler problem does not affect any versions of clang, and In addition to that, any versions of apple clang seems to support "native" architecture, but may not support AVX related flags including "-mno-avx".

Any versions of apple clang seem to support "native" architecture, but an apple lvm-gcc-4.2, which potentially be a default compiler, does not support it.

The "-ftree-vectorize" flag is a gcc-specific flag (I should have notice it before the upload of my previous diff, though), which could be a cause of unnecessary warning on a clang.

I updated your diff. If it looks okay, I will send a commit request of it. Thank you very much.

[NicosPavlov]

Right, I also missed it. The patch seems fine to me. If it is alright like this for you, I could commit it right away, without having to send a commit request.

[daitakahashi]

I think there are no problems left on the patch, so please commit it. Thank you very much.

[NicosPavlov]

Committed in r114154 along with a rev bump as it changes installed files. Thanks for your help on the patch.