The previous installPhase was only using `make install`, while the real
target needed is `make install-all`. This installs many missing tools
under `$out/libexec/`, such as the missing `gnatwhy3` binary, which was
the root cause of #208830.
With this, gnatprove can now successfully discharge and prove things
with solvers like Z3, etc.
And, because it also includes `why3server`, we don't need to use
wrapProgram on it anymore, either!
Closes#208830
Signed-off-by: Austin Seipp <aseipp@pobox.com>
