Index: CMakeLists.txt
===================================================================
--- CMakeLists.txt
+++ CMakeLists.txt
@@ -441,6 +441,13 @@
   add_definitions(-DCLANG_ENABLE_STATIC_ANALYZER)
 endif()
 
+set(OPENMP_DEFAULT_LIB "" CACHE STRING
+  "OpenMP library used with -fopenmp.")
+
+if( OPENMP_DEFAULT_LIB )
+  add_definitions( -DOPENMP_DEFAULT_LIB="${OPENMP_DEFAULT_LIB} " )
+endif()
+
 # Clang version information
 set(CLANG_EXECUTABLE_VERSION
      "${CLANG_VERSION_MAJOR}.${CLANG_VERSION_MINOR}" CACHE STRING
Index: lib/Driver/Tools.cpp
===================================================================
--- lib/Driver/Tools.cpp
+++ lib/Driver/Tools.cpp
@@ -6279,16 +6279,23 @@
   Args.AddAllArgs(CmdArgs, options::OPT_L);
 
   LibOpenMP UsedOpenMPLib = LibUnknown;
-  if (const Arg *A = Args.getLastArg(options::OPT_fopenmp_EQ)) {
-    UsedOpenMPLib = llvm::StringSwitch<LibOpenMP>(A->getValue())
+  auto OpenMPStringToVersion = [](StringRef OpenMPString) {
+    return llvm::StringSwitch<LibOpenMP>(OpenMPString)
         .Case("libgomp",  LibGOMP)
         .Case("libiomp5", LibIOMP5)
         .Default(LibUnknown);
+  };
+  if (const Arg *A = Args.getLastArg(options::OPT_fopenmp_EQ)) {
+    UsedOpenMPLib = OpenMPStringToVersion(A->getValue());
     if (UsedOpenMPLib == LibUnknown)
       getToolChain().getDriver().Diag(diag::err_drv_unsupported_option_argument)
         << A->getOption().getName() << A->getValue();
   } else if (Args.hasArg(options::OPT_fopenmp)) {
+#if defined(OPENMP_DEFAULT_LIB)
+    UsedOpenMPLib = OpenMPStringToVersion(OPENMP_DEFAULT_LIB);
+#else
     UsedOpenMPLib = LibIOMP5;
+#endif
   }
   switch (UsedOpenMPLib) {
   case LibGOMP: