Rename MSVC top-level folder to avoid name collision.

If you have two folders with the same name but different cases,
MSBuild gets confused and generates an error when building
from within Visual Studio.

This patch renames it so that the cases of all folders named
"LLDB tests" match.

Patch by Jonathan Meier
Differential Revision: http://reviews.llvm.org/D16150

llvm-svn: 257684