Remove change to set SDKROOT when building compiler-rt on Darwin.
Remove change to set SDKROOT when building compiler-rt on Darwin.

This reverts the runtime library portion of r194168. As of r221621,
the libclang_rt libraries for Darwin build with explicit SDK options
so there is no need to set SDKROOT here.

git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@221625 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,llvm-mirror/clang,apple/swift-clang,llvm-mirror/clang,llvm-mirror/clang,apple/swift-clang,llvm-mirror/clang,apple/swift-clang,llvm-mirror/clang,llvm-mirror/clang,apple/swift-clang,llvm-mirror/clang,apple/swift-clang,llvm-mirror/clang,llvm-mirror/clang