This issue was solved with changeset r36499.
Perry, thank you for reporting this issue.
Your contribution to Ruby is greatly appreciated.
May Ruby be with you.
configure.in: LIBPATH on AIX
configure.in (LIBPATHENV): LIBPATH is used on AIX, but not
SHLIB_PATH which was carelessly copied from HP/UX. suggested by
Perry Smith at [ruby-core:46397]. [Bug #6728]