Move the 'linker-script-test' binary to the tools directory.

The canonical LLVM directory arrangement places binaries in the 'utils/'
tree when they are used as part of building the project. For example,
the tblgen binaries are built out of 'utils/' trees.

Tools which are not used by any other part of the build, including
testing utilities, are just in the 'tools' directory. For example, in
Clang we have 'c-index-test' which is exactly the same kind of thing as
'linker-script-test'.

Differential Revision: http://reviews.llvm.org/D8269

llvm-svn: 231973