This isn't strictly needed, but this matches how MSVC lib.exe writes to
archives, so this makes llvm-lib more compatible and simplifies comparing
output between tools.
Reviewed By: hans
Differential Revision: https://reviews.llvm.org/D143536
Similarly to SVN r317189 for llvm-dlltool, these are probably
easier to find in a tools subdirectory with a name identical to
the tool, than in a toplevel directory with a different name.
This matches the move of LibDriver itself in SVN r302995.
Differential Revision: https://reviews.llvm.org/D39531
llvm-svn: 317262