Introduce a PCHContainerOperations interface (NFC).

A PCHContainerOperations abstract interface provides operations for
creating and unwrapping containers for serialized ASTs (precompiled
headers and clang modules). The default implementation is
RawPCHContainerOperations, which uses a flat file for the output.

The main application for this interface will be an
ObjectFilePCHContainerOperations implementation that uses LLVM to
wrap the module in an ELF/Mach-O/COFF container to store debug info
alongside the AST.

rdar://problem/20091852

llvm-svn: 240225

clang/lib/Frontend/ASTMerge.cpp

@@ -45,8 +45,10 @@ void ASTMergeAction::ExecuteAction() {
                                     new ForwardingDiagnosticConsumer(
                                           *CI.getDiagnostics().getClient()),
                                     /*ShouldOwnClient=*/true));
-    std::unique_ptr<ASTUnit> Unit = ASTUnit::LoadFromASTFile(
-        ASTFiles[I], Diags, CI.getFileSystemOpts(), false);
+    std::unique_ptr<ASTUnit> Unit =
+        ASTUnit::LoadFromASTFile(ASTFiles[I], CI.getPCHContainerOperations(),
+                                 Diags, CI.getFileSystemOpts(), false);
+
     if (!Unit)
       continue;