Revert to per-language libpath computation on AIX.

Revert to per-language libpath computation on AIX.

* libltdl/m4/libtool.m4 (_LT_SYS_MODULE_PATH_AIX): Accept
tagname argument.  Use global cache variable lt_cv_aix_libpath
to override per-language tag variables for the libpath value.
Fix the sed script to remove trailing space.
(_LT_LINKER_SHLIBS, _LT_LANG_CXX_CONFIG): Pass tag argument to
_LT_SYS_MODULE_PATH_AIX.
Tracked down and reported by Rainer Tammer.

Signed-off-by: Ralf Wildenhues <Ralf.Wildenhues@gmx.de>