Enable chained precompiled headers for use with precompiled preambles

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@115260 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Frontend/ASTUnit.cpp b/lib/Frontend/ASTUnit.cpp
index bd7e712..19d1690 100644
--- a/lib/Frontend/ASTUnit.cpp
+++ b/lib/Frontend/ASTUnit.cpp
@@ -1158,9 +1158,7 @@
   
   // Tell the compiler invocation to generate a temporary precompiled header.
   FrontendOpts.ProgramAction = frontend::GeneratePCH;
-  // FIXME: Set ChainedPCH unconditionally, once it is ready.
-  if (::getenv("LIBCLANG_CHAINING"))
-    FrontendOpts.ChainedPCH = true;
+  FrontendOpts.ChainedPCH = true;
   // FIXME: Generate the precompiled header into memory?
   FrontendOpts.OutputFile = PreamblePCHPath;