Serialize `#pragma comment`.

`#pragma comment` was handled by Sema calling a function on ASTConsumer, and
CodeGen then implementing this function and writing things to its output.

Instead, introduce a PragmaCommentDecl AST node and hang one off the
TranslationUnitDecl for every `#pragma comment` line, and then use the regular
serialization machinery. (Since PragmaCommentDecl has codegen relevance, it's
eagerly deserialized.)

http://reviews.llvm.org/D17799

llvm-svn: 262493
diff --git a/clang/lib/AST/DeclBase.cpp b/clang/lib/AST/DeclBase.cpp
index d41d25f..91bc809 100644
--- a/clang/lib/AST/DeclBase.cpp
+++ b/clang/lib/AST/DeclBase.cpp
@@ -641,6 +641,7 @@
     case FileScopeAsm:
     case StaticAssert:
     case ObjCPropertyImpl:
+    case PragmaComment:
     case Block:
     case Captured:
     case TranslationUnit: