Travis CI builds using both clang and gcc

[qqii]

@jnterry is this intended behaviour?

118

[jnterry]

Yes - the idea was that testing on multiple compilers would be more likely to pick up any any issues where we are relying on gcc specific behaviour.

This makes it less likely we break windows etc without having to go through the pain of setting up windows ci, which is much more effort than just turning on clang builds