[CMake] Include llvm-libtool-darwin in Fuchsia toolchain

We want to use this tool in our build.

Differential Revision: https://reviews.llvm.org/D111366

Author: petrhosek

clang/cmake/caches/Fuchsia-stage2.cmake

@@ -270,6 +270,7 @@ set(LLVM_TOOLCHAIN_TOOLS
   llvm-ifs
   llvm-gsymutil
   llvm-lib
+  llvm-libtool-darwin
   llvm-lipo
   llvm-mt
   llvm-nm