macOS package: fix unresolved symbols in qmc_sequence MEX

Fixes https://forum.dynare.org/t/invalid-mex-file-whe-running-sensitivity-analysis-m1-mac-6-1/25829

It seems that meson does not link libquadmath (which is needed by libgfortran).
When doing dynamic linking, this is not an issue since the dynamic linker loads
libquadmath recursively after loading libgfortran. But when doing static linking,
libquadmath needs to be explicitly linked.

Not yet clear at this point: why isn’t this needed under Linux and Windows?

meson.build

@@ -390,6 +390,16 @@ qmc_sequence_mex_kwargs = mex_kwargs
 if get_option('prefer_static') and host_machine.system() == 'windows'
   qmc_sequence_mex_kwargs += { 'link_args' : qmc_sequence_mex_kwargs.get('link_args') + [ '-Wl,-Bstatic', '-lgfortran', '-Wl,-Bdynamic' ] }
 endif
+# Hack for statically linking libquadmath
+# Fixes https://forum.dynare.org/t/invalid-mex-file-whe-running-sensitivity-analysis-m1-mac-6-1/25829
+# It seems that meson does not link libquadmath (which is needed by libgfortran).
+# When doing dynamic linking, this is not an issue since the dynamic linker loads
+# libquadmath recursively after loading libgfortran. But when doing static linking,
+# libquadmath needs to be explicitly linked.
+# FIXME: Why isn’t this needed under Linux and Windows?
+if get_option('prefer_static') and host_machine.system() == 'darwin'
+  qmc_sequence_mex_kwargs += { 'link_args' : qmc_sequence_mex_kwargs.get('link_args') + [ '-lquadmath' ] }
+endif
 shared_module('qmc_sequence', qmc_sequence_src, kwargs : qmc_sequence_mex_kwargs, dependencies : [ blas_dep, openmp_dep ])
 
 shared_module('kalman_steady_state', 'mex/sources/kalman_steady_state/kalman_steady_state.cc', kwargs : mex_kwargs, dependencies : slicot_dep)