Revert "cmake: use llvm dir variables for clang/utils/hmaptool"

As discussed on the review, this change breaks the standalone
clang build. When building against an installed LLVM, the
LLVM_TOOLS_BINARY_DIR cmake variable points to the location of
the installed LLVM tools, not to the cmake build directory. This
means that we would end up trying to move hmaptool into something
like /usr/bin as part of the normal build, while this should only
be happening when running an install target.

This reverts commit bf1ab1f0.