Index: llvm/trunk/cmake/modules/LLVMExternalProjectUtils.cmake
===================================================================
--- llvm/trunk/cmake/modules/LLVMExternalProjectUtils.cmake
+++ llvm/trunk/cmake/modules/LLVMExternalProjectUtils.cmake
@@ -143,6 +143,7 @@
     CMAKE_ARGS ${${nameCanon}_CMAKE_ARGS}
                ${compiler_args}
                -DCMAKE_INSTALL_PREFIX=${CMAKE_INSTALL_PREFIX}
+               -DCMAKE_SYSROOT=${CMAKE_SYSROOT}
                -DLLVM_BINARY_DIR=${PROJECT_BINARY_DIR}
                -DLLVM_CONFIG_PATH=$<TARGET_FILE:llvm-config>
                -DLLVM_ENABLE_WERROR=${LLVM_ENABLE_WERROR}