
Consider switching to a pkg-config-based approach to handle the linking
dependencies.

For context, this was suggested by Tomas Kalibera in an email from March 4,
2025:

  I am sorry to report that Rhtslib needs to be updated to work with an
  upcoming version of Rtools (Rtools45), where libcurl depends newly on
  nghttp2 (and nghttp2 has been newly added to Rtools).

  I've created a patch that extends Rhtslib to do it the same way this has
  been done before in the package, so optionally linking nghttp2 when it is
  available. With the patch, the package builds fine on my system. However,
  it might make sense to switch to pkg-config, so that next time the
  dependencies change (and in case of curl it is quite common), you
  hopefully don't have to update the package.

