Add a little hack to emulate a clang crash, so the diagnostics generator can be
tested.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@155205 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/tools/driver/driver.cpp b/tools/driver/driver.cpp
index 8c05fff..a077384 100644
--- a/tools/driver/driver.cpp
+++ b/tools/driver/driver.cpp
@@ -475,6 +475,10 @@
   if (C.get())
     Res = TheDriver.ExecuteCompilation(*C, FailingCommand);
 
+  // Force a crash to test the diagnostics.
+  if(::getenv("FORCE_CLANG_DIAGNOSTICS_CRASH"))
+     Res = -1;
+
   // If result status is < 0, then the driver command signalled an error.
   // In this case, generate additional diagnostic information if possible.
   if (Res < 0)