Generate coverage reports for XS code automatically

[nwellnhof]

Devel::Cover already works nicely with XS code. All that's needed is to add the necessary compiler and linker options. This patch works for me with an EU::MM based project. Similar changes are required for M::B projects.

[rfdrake]

+1

I think with this patch it would work for distzilla as well.

[DrHyde]

I too would find this useful