[CMake] Only build the simulator builtins if you're also building the device builtins.
[CMake] Only build the simulator builtins if you're also building the device builtins.

This matters because simulator builtins get lipo'd together with the device builtins into a single static archive per-platform.

git-svn-id: c199f293c43da69278bea8e88f92242bf3aa95f7@249056 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/compiler-rt,llvm-mirror/compiler-rt,llvm-mirror/compiler-rt,llvm-mirror/compiler-rt,llvm-mirror/compiler-rt