Resolve "device" definition dependency lazily.
Mark machdep files.
Pass stricter build.
- Explicitly describe that kvm(3) is used when -M/-N option is used since
  nowadays sysctl(3) is the default information retrieval method.
- Fix description about default value for -N; it is no longer a single value
  these days, so just say see kvm_openfiles(3) rahter than repeating
  several lines description here.
Fix _sqrtl alias
Define filesystem attributes with vfs dependency.
Seems we need both sqrtl and _sqrtl as a weak alias - something must be
wrong namespapce wise here, but this should make it build for now.
Probably agp_apple is never used.
Don't define WSDISPLAY_* without wsdisplay.
Need powl as alias as well
Missing midi attachment.