Add LLVM_TOOLS_BINARY_DIR variable to LLVMConfig.cmake so clients
of LLVM using CMake can easily find the tools directory.

LLVM_BUILD_TOOLS_BINARY_DIR was removed because it is now
superfluous.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@213674 91177308-0d34-0410-b5e6-96231b3b80d8