This fixes a few problems in the powerpc ld configury.
1) Using powerpc*le-* to test for powerpcle and powerpc64le would
incorrectly match a target triple like powerpc-apple-elf.
2) In the same vein, *64* could match 64 in the user supplied MANUF-OS
part of the target triple.
3) tooldir vars were missing, and some target aliases would result in
ridiculous values for those tdir_* vars given.
4) Since 2016-04-25, BE support was added automatically when asking
for an LE target. If that is a good idea, then so is adding LE
support when asking for BE.
* configure.tgt (powerpc*-*-linux* et al): Rewrite, adding LE
support for BE. First output all target endian configury
values, then opposite endian. Handle more tooldirs. Fix
bogus matches with strings in MANUF-OS part of target triple.