Use libstc++ for the name of bionic's STL.

It is libstdc++.so, after all, and the naming makes sense for the host
this way (since it also uses libstdc++).

Change-Id: If37ffa015f7967a928ea47a290363d7696c4ce35
Fix breakage for x86_64 static executables.

Yikes. Don't know how this slipped through code review.

I had actually mentioned a need for cleanup in this part of the build
system earlier, since the amount of duplication between
transform-o-to-* for each arch means we might fix things incorrectly
in one of them (as I've just shown). Similarly, code reviewers are
likely to skim each one after the first if they all look close enough
(which is presumably what happened here).

Change-Id: I9b85914510f0b114485021deb97f42740712aae5