[arcmt] Introduce new '-ccc-arcmt-migrate <path>' ARC migration driver option.

This is a new mode of migration, where we avoid modifying the original files but
we emit temporary files instead.

<path> will be used to keep migration process metadata. Currently the temporary files
that are produced are put in the system's temp directory but we can put them
in the <path> if is necessary.

Also introduce new ARC migration functions in libclang whose only purpose,
currently, is to accept <path> and provide pairs of original file/transformed file
to map from the originals to the files after transformations are applied.

Finally introduce the c-arcmt-test utility that exercises the new libclang functions,
update arcmt-test, and add tests for the whole process.

rdar://9735086.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@134844 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Frontend/CompilerInvocation.cpp b/lib/Frontend/CompilerInvocation.cpp
index ebc3340..02a5088 100644
--- a/lib/Frontend/CompilerInvocation.cpp
+++ b/lib/Frontend/CompilerInvocation.cpp
@@ -431,6 +431,13 @@
   case FrontendOptions::ARCMT_Modify:
     Res.push_back("-arcmt-modify");
     break;
+  case FrontendOptions::ARCMT_Migrate:
+    Res.push_back("-arcmt-migrate");
+    break;
+  }
+  if (!Opts.ARCMTMigrateDir.empty()) {
+    Res.push_back("-arcmt-migrate-directory");
+    Res.push_back(Opts.ARCMTMigrateDir);
   }
 
   bool NeedLang = false;
@@ -1251,7 +1258,8 @@
 
   Opts.ARCMTAction = FrontendOptions::ARCMT_None;
   if (const Arg *A = Args.getLastArg(OPT_arcmt_check,
-                                     OPT_arcmt_modify)) {
+                                     OPT_arcmt_modify,
+                                     OPT_arcmt_migrate)) {
     switch (A->getOption().getID()) {
     default:
       llvm_unreachable("missed a case");
@@ -1261,8 +1269,12 @@
     case OPT_arcmt_modify:
       Opts.ARCMTAction = FrontendOptions::ARCMT_Modify;
       break;
+    case OPT_arcmt_migrate:
+      Opts.ARCMTAction = FrontendOptions::ARCMT_Migrate;
+      break;
     }
   }
+  Opts.ARCMTMigrateDir = Args.getLastArgValue(OPT_arcmt_migrate_directory);
 
   InputKind DashX = IK_None;
   if (const Arg *A = Args.getLastArg(OPT_x)) {