Avoid using /* in the comment (which starts a C comment)

Since this header is included in .F90 files (which are preprocessed,
vs. .f90 files, which are *not* preprocessed), we don't want to
accidentally start C-style comments, which are recognized by some
Fortran compiler preprocessors (e.g., Absoft).
Add weak symbol #defines.

Fixes compile errors if you compile --without-weak-symbols.
Remove unused files.
Fix --without-hwloc build