Index: CMakeLists.txt
===================================================================
--- CMakeLists.txt
+++ CMakeLists.txt
@@ -225,6 +225,17 @@
 # Warnings to turn off for all libraries, not just sanitizers.
 append_string_if(COMPILER_RT_HAS_WUNUSED_PARAMETER_FLAG -Wno-unused-parameter CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
 
+if (CMAKE_LINKER MATCHES "link.exe$")
+  # We put empty object files in archives, which causes MSVC's linker to
+  # complain about these objects not defining any previously undefined
+  # symbols. Since we do it on purpose, this only creates noise during
+  # the build process, so we suppress the warnings here. Ideally, we would
+  # pass this flag only for the libraries that need it, but CMake doesn't
+  # seem to have a way to set linker flags for individual static libraries,
+  # so we enable the suppression flag for the whole compiler-rt project.
+  append("/IGNORE:4221" CMAKE_STATIC_LINKER_FLAGS)
+endif()
+
 add_subdirectory(include)
 
 set(COMPILER_RT_LIBCXX_PATH ${LLVM_MAIN_SRC_DIR}/projects/libcxx)