[CMake][Fuchsia] Pass -ldl -lpthread LDFLAGS to second stage

We're using static libc++ for the second stage which requires explicitly
linking -ldl and -lpthread.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@353853 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed