Autotools update

Adds --disable-vec option to add the following flags:

• GCC: -fno-tree-vectorize
• ICC: -no-vec -no-simd
• CLANG: -fno-vectorize -fno-slp-vectorize"

There is no --enable-vec, that is a noop.

James please test that these flags work and do as you expect. When happy reassign to @matthieu to do the merge request (OK to delete the branch). Should resolve #105 (closed).

mentioned in issue #105 (closed)

I've tested it on COSMA5 and SuperMUC and get the correct flags for both gcc and icc.

Reassigned to @matthieu

Thanks for checking this.

mentioned in commit 98fb00bc

Status changed to merged