The declaration for a function is incorrect; the implementation of it is missing a const. Adding a const to the implementation (line 335) is enough to fix this particular issue.
rs6000-core.c:280:19: warning: type qualifiers ignored on function return type [-Wignored-qualifiers] const bfd_cleanup rs6000coff_core_p (bfd *abfd); ^~~~~~~~~~~~~~~~~ rs6000-core.c:336:1: error: conflicting types for 'rs6000coff_core_p' rs6000coff_core_p (bfd *abfd) ^~~~~~~~~~~~~~~~~ rs6000-core.c:280:19: note: previous declaration of 'rs6000coff_core_p' was here const bfd_cleanup rs6000coff_core_p (bfd *abfd); ^~~~~~~~~~~~~~~~~