Avoid crashing if a directory has no pch files.

Should fix some of the bots that have assertions disabled.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@187329 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Frontend/FrontendAction.cpp b/lib/Frontend/FrontendAction.cpp
index 60e6156..075fe93 100644
--- a/lib/Frontend/FrontendAction.cpp
+++ b/lib/Frontend/FrontendAction.cpp
@@ -455,6 +455,8 @@
 
 void ASTFrontendAction::ExecuteAction() {
   CompilerInstance &CI = getCompilerInstance();
+  if (!CI.hasPreprocessor())
+    return;
 
   // FIXME: Move the truncation aspect of this into Sema, we delayed this till
   // here so the source manager would be initialized.