Compile GALAHAD_jll.jl with HSL_jll.jl

[amontoison]

One of the initial goals of libHSL was to facilitate the utilization of HSL routines in GALAHAD by consolidating them into a single static/shared library libhsl.
This approach works well when using the Meson build system, as we only need to specify the options -Dlibhsl_path=... and -Dlibhsl_modules=... to indicate the path to the library / Fortran modules when compiling GALAHAD.
However, this requires compiling GALAHAD on our computer.

For Julia users, we offer a precompiled version, GALAHAD_jll.jl, enabling the use of the Julia interface, GALAHAD.jl, without any compilation requirements and with all open-source dependencies (MUMPS, PASTIX, METIS, etc.).
Although we cannot compile it with the official libhsl.so, we could compile it with the provided dummy version from ralna/libHSL, available as HSL_jll.jl.
Currently, ralna/libHSL only offers one routine (LIBHSL_isfunctional) required by HSL.jl, but we could augment it with dummy files for all symbols and modules necessary for GALAHAD.

If successful, this would mean that installing the official HSL_jll.jl package provided with the source of libHSL would automatically enable the use of HSL routines in GALAHAD.jl like it is already the case in Ipopt.jl.

[amontoison]

Done in JuliaPackaging/Yggdrasil#9049