Support Intel compiler

[MattWindsor91]

We should make the tester able to target the Intel compiler (icc).

From playing around with icc and looking at the help documents:

• We should be able to implement most of the Intel compiler interface on top of the existing gcc support;
• We'd want to teach the tester about some of the more esoteric optimisation flags icc supports that gcc doesn't, eg the whole difference between -x, -ax, -arch, -march etc;
• If we're targeting Windows at any point, we'd need to teach it the different argument convention on Windows;
• We'd probably need to indirect through a Bash script that sources the requisite variables and invokes the compiler, but I don't think the tester would need to know about this.

[MattWindsor91]

So far, using icc as a gcc style compiler through a wrapper script seems to work, so this support would mainly be teaching the optimisation selector about icc's various exciting different optimisation levels.