Forward -bitcode_process_mode to ld64 in marker-only mode

[mehdi_amini]

Add a test

[steven_wu]

LGTM

cfe/trunk/lib/Driver/Tools.cpp

if (A->getOption().matches(options::OPT_fpie) ||
       CmdArgs.push_back("-pie");
     else
       CmdArgs.push_back("-no_pie");
   }
 
   // for embed-bitcode, use -bitcode_bundle in linker command
   if (C.getDriver().embedBitcodeEnabled()) {
     // Check if the toolchain supports bitcode build flow.
-    if (MachOTC.SupportsEmbeddedBitcode())
+    if (MachOTC.SupportsEmbeddedBitcode()) {
       CmdArgs.push_back("-bitcode_bundle");
-    else
+      if (C.getDriver().embedBitcodeMarkerOnly() && Version[0] >= 278) {
+        CmdArgs.push_back("-bitcode_process_mode");
+        CmdArgs.push_back("marker");
+      }
+    } else
       D.Diag(diag::err_drv_bitcode_unsupported_on_toolchain);
   }
 
   Args.AddLastArg(CmdArgs, options::OPT_prebind);
   Args.AddLastArg(CmdArgs, options::OPT_noprebind);
   Args.AddLastArg(CmdArgs, options::OPT_nofixprebinding);
   Args.AddLastArg(CmdArgs, options::OPT_prebind__all__twolevel__modules);
   Args.AddLastArg(CmdArgs, options::OPT_read__only__relocs);

cfe/trunk/test/Driver/embed-bitcode.c

 // RUN: %clang -c %s -flto -fembed-bitcode 2>&1 -### | FileCheck %s -check-prefix=CHECK-LTO
 // RUN: %clang -c %s -flto=full -fembed-bitcode 2>&1 -### | FileCheck %s -check-prefix=CHECK-LTO
 // RUN: %clang -c %s -flto=thin -fembed-bitcode 2>&1 -### | FileCheck %s -check-prefix=CHECK-LTO
 // CHECK-LTO: -cc1
 // CHECK-LTO: -emit-llvm-bc
 // CHECK-LTO-NOT: warning: argument unused during compilation: '-fembed-bitcode'
 // CHECK-LTO-NOT: -cc1
 // CHECK-LTO-NOT: -fembed-bitcode=all
+// RUN: touch %t.o
+// RUN: %clang  %t.o -fembed-bitcode  -fembed-bitcode-marker -mlinker-version=277  2>&1 -### | FileCheck %s -check-prefix=CHECK-LTO-MARKER-277
+// RUN: %clang  %t.o -fembed-bitcode  -fembed-bitcode-marker -mlinker-version=278  2>&1 -### | FileCheck %s -check-prefix=CHECK-LTO-MARKER-278
+// CHECK-LTO-MARKER-277-NOT: bitcode_process_mode
+// CHECK-LTO-MARKER-278: bitcode_process_mode
+
+
 
 // RUN: %clang -c %s -fembed-bitcode-marker -fintegrated-as 2>&1 -### | FileCheck %s -check-prefix=CHECK-MARKER
 // CHECK-MARKER: -cc1
 // CHECK-MARKER: -emit-obj
 // CHECK-MARKER: -fembed-bitcode=marker
 // CHECK-MARKER-NOT: -cc1
 
 // RUN: %clang -target armv7-apple-darwin -miphoneos-version-min=6.0 %s -fembed-bitcode=all -fintegrated-as 2>&1 -### | FileCheck %s -check-prefix=CHECK-LINKER