Falling back to static linking is confusing

[umanwizard]

Even without the static flag, if we can't find bzip2 via pkg-config, we fall back to static linking. This is confusing and leads to hard-to-debug differences between binaries built from the same source depending on exactly what OS they were compiled for.

IMO, failing to find the dynamic library when the static option has not been requested should be a hard failure (perhaps with a helpful error message about enabling static if you want to statically link a vendored libbzip2)