modules are not found when installing suil in /usr/lib64 (as opposed to /usr/local/lib)

After installing suil 0.10.14 I can't open plugin GUI in ardour. The reported error is

suil error: Failed to open module /usr/local/lib/suil-0/libsuil_x11_in_gtk2.so (/usr/local/lib/suil-0/libsuil_x11_in_gtk2.so: cannot open shared object file: No such file or directory)

Suil was installed system-wide by the Gentoo package manager. The latter passed the options --libdir lib64 --prefix /usr to meson. Hence the modules are installed in /usr/lib64/suil-0/ However, suil has a default hardcoded path for SUIL_MODULE_DIR set to "/usr/local/lib/suil-0"

Adding the following in meson.build fixes the issue

extra_c_args += ['-DSUIL_MODULE_DIR="' + get_option('prefix') / suil_module_dir + '"']

I've successfully used this on linux. Maybe the above should not be added on Windows. I don't have a windows machine to test what value would be passed.