Uses architecture dependent library path on alpine linux

Installing tango-idl in version ada81f82 (Merge pull request #11 (closed) from beenje/license, 2021-01-08) on alpine linux does the following:

Install the project...
-- Install configuration: ""
-- Up-to-date: /usr/local/include/tango.idl
-- Up-to-date: /usr/local/lib64/pkgconfig/tangoidl.pc

whereas on debian it install tangoidl.pc into /usr/local/lib/pkgconfig/tangoidl.pc.

It think we should fix that as the pkgconfig file we are providing is architecture independent.