Hi.
This patch adds support for getting the CPU features in libgccjit (bug
112466)

There's a TODO in the test:
I'm not sure how to test that gcc_jit_target_info_arch returns the
correct value since it is dependant on the CPU.
Any idea on how to improve this?

Also, I created a CStringHash to be able to have a
std::unordered_set<const char *>. Is there any built-in way of doing
this?

Thanks for the review.