Index: CMakeLists.txt
===================================================================
--- CMakeLists.txt
+++ CMakeLists.txt
@@ -305,6 +305,18 @@
 # so they don't get transformed into -Wno and -errors respectivly.
 remove_flags(-Wno-pedantic -pedantic-errors -pedantic)
 
+# FIXME: this is cribbed from HandleLLVMOptions.cmake.
+if(LIBCXX_STANDALONE_BUILD)
+  # Pass -Wl,-z,defs. This makes sure all symbols are defined. Otherwise a DSO
+  # build might work on ELF but fail on MachO/COFF.
+  if(NOT (${CMAKE_SYSTEM_NAME} MATCHES "Darwin" OR WIN32 OR CYGWIN OR
+          ${CMAKE_SYSTEM_NAME} MATCHES "FreeBSD" OR
+          ${CMAKE_SYSTEM_NAME} MATCHES "OpenBSD") AND
+     NOT LLVM_USE_SANITIZER)
+    set(CMAKE_SHARED_LINKER_FLAGS "${CMAKE_SHARED_LINKER_FLAGS} -Wl,-z,defs")
+  endif()
+endif()
+
 # Required flags ==============================================================
 set(LIBCXX_STANDARD_VER c++11 CACHE INTERNAL "internal option to change build dialect")
 add_compile_flags_if_supported(-std=${LIBCXX_STANDARD_VER})