Vips: make core deps recommended

libvips has a lot of dependencies: some are used to implement core
functions, some are used to add support for less-used file formats.
Previously all non-required dependencies were :optional, so, by default,
libvips was missing a lot of features.

This patch tags dependencies which are used to implement vips operations
and support for common file formats as :recommended and leaves those
which are used for less-common file formats as :optional.

Closes #707.
Scalapack: add head.
Mumps: select compiler based on :mpi.
Ipopt: Upgrade to 3.11.7 and build fixes.

- Remove MPI compilers from environment as they crash the linker
- Apply patch if Mumps was built in parallel
- Add option to skip build-time tests.

Closes #656.
Catch up with upstream audit changes
ipopt: don't do work in class scope