diff --git a/llvm/runtimes/CMakeLists.txt b/llvm/runtimes/CMakeLists.txt
--- a/llvm/runtimes/CMakeLists.txt
+++ b/llvm/runtimes/CMakeLists.txt
@@ -245,6 +245,7 @@
                                         -DCMAKE_ASM_COMPILER_TARGET=${TARGET_TRIPLE}
                                         -DCMAKE_C_COMPILER_WORKS=ON
                                         -DCMAKE_ASM_COMPILER_WORKS=ON
+                                        -DCMAKE_SYSTEM_NAME=${CMAKE_SYSTEM_NAME}
                              PASSTHROUGH_PREFIXES COMPILER_RT
                              USE_TOOLCHAIN
                              ${EXTRA_ARGS})
@@ -390,6 +391,7 @@
                                         -DCMAKE_C_COMPILER_WORKS=ON
                                         -DCMAKE_CXX_COMPILER_WORKS=ON
                                         -DCMAKE_ASM_COMPILER_WORKS=ON
+                                        -DCMAKE_SYSTEM_NAME=${CMAKE_SYSTEM_NAME}
                              PASSTHROUGH_PREFIXES LLVM_ENABLE_RUNTIMES
                                                   ${ARG_PREFIXES}
                              EXTRA_TARGETS ${extra_targets}