[cmake] Include the llvm-locstats target when

utils and tools are not being built.

This was uncovered by: https://reviews.llvm.org/D71611
Which added llvm-locstats to the test dependencies.

Previously the build target was only added if you
were building tools. This meant that you couldn't
configure at all if you had LLVM_BUILD_TOOLS=OFF.

Differential revision: https://reviews.llvm.org/D71695