Index: cmake/modules/HandleLLVMOptions.cmake
===================================================================
--- cmake/modules/HandleLLVMOptions.cmake
+++ cmake/modules/HandleLLVMOptions.cmake
@@ -229,6 +229,9 @@
   # MinGW warns if -fvisibility-inlines-hidden is used.
   check_cxx_compiler_flag("-fvisibility-inlines-hidden" SUPPORTS_FVISIBILITY_INLINES_HIDDEN_FLAG)
   append_if(SUPPORTS_FVISIBILITY_INLINES_HIDDEN_FLAG "-fvisibility-inlines-hidden" CMAKE_CXX_FLAGS)
+
+  check_cxx_compiler_flag("-fvisibility=protected" SUPPORTS_FVISIBILITY_PROTECTED_FLAG)
+  append_if(SUPPORTS_FVISIBILITY_INLINES_HIDDEN_FLAG "-fvisibility=protected" CMAKE_CXX_FLAGS)
 endif()
 
 if( CMAKE_SIZEOF_VOID_P EQUAL 8 AND NOT WIN32 )
Index: include/llvm/Support/Compiler.h
===================================================================
--- include/llvm/Support/Compiler.h
+++ include/llvm/Support/Compiler.h
@@ -101,8 +101,10 @@
 #if (__has_attribute(visibility) || LLVM_GNUC_PREREQ(4, 0, 0)) &&              \
     !defined(__MINGW32__) && !defined(__CYGWIN__) && !defined(LLVM_ON_WIN32)
 #define LLVM_LIBRARY_VISIBILITY __attribute__ ((visibility("hidden")))
+#define LLVM_PREEMPTIBLE_VISIBILITY __attribute__ ((visibility("default")))
 #else
 #define LLVM_LIBRARY_VISIBILITY
+#define LLVM_PREEMPTIBLE_VISIBILITY
 #endif
 
 #if defined(__GNUC__)
Index: utils/unittest/UnitTestMain/TestMain.cpp
===================================================================
--- utils/unittest/UnitTestMain/TestMain.cpp
+++ utils/unittest/UnitTestMain/TestMain.cpp
@@ -21,7 +21,7 @@
 
 const char *TestMainArgv0;
 
-int main(int argc, char **argv) {
+LLVM_PREEMPTIBLE_VISIBILITY int main(int argc, char **argv) {
   llvm::sys::PrintStackTraceOnErrorSignal(argv[0],
                                           true /* Disable crash reporting */);