bzip3 package should be compiled with clang

The new bzip3 package (thanks Grigory!) has been setup upstream such that it can be compiled with either clang or gcc, but there is a significant performance bump when compiled with clang. Given that compression performance is a major goal of the project this is a significant issue.

All that is required is to supply clang as a build time dependency. If the build system has it it should find and prefer it during configure. You can also force it so that it errors if not found by explicitly setting ./configure CC=clang, but I think the issue with the current package is just that it was not provided as a makedepends.

The build log will show when it gets picked up:

checking for aarch64-alpine-linux-musl-clang... gcc
[...]
checking whether gcc is Clang... no