How to set linker in cmake of llvm project?

I build the newest llvm from svn on iMac by set compiler and compiler flag as follows,

cmake -DCMAKE_CXX_COMPILER=clang++ -DCMAKE_C_COMPILER=clang -DCMAKE_CXX_FLAGS=-std=c++11\ -stdlib=libc++ -DCMAKE_BUILD_TYPE=Debug -G "Xcode"

But how to set LINK to clang++? The default is ld in Xcode of llvm project.

Jonathan