Initial implementation of a record-level bitcode fuzzer.

lib/Bitcode/NaCl/TestUtils/NaClBitcodeMungeWriter.cpp

Index: lib/Bitcode/NaCl/TestUtils/NaClBitcodeMungeWriter.cpp
diff --git a/lib/Bitcode/NaCl/TestUtils/NaClBitcodeMungeWriter.cpp b/lib/Bitcode/NaCl/TestUtils/NaClBitcodeMungeWriter.cpp
index da2907b1a9ee44af02ac208e9d5321f59451f7af..49f3cc28cef22c64751aa26497a1c86fa8b5b24b 100644
--- a/lib/Bitcode/NaCl/TestUtils/NaClBitcodeMungeWriter.cpp
+++ b/lib/Bitcode/NaCl/TestUtils/NaClBitcodeMungeWriter.cpp
@@ -377,6 +377,12 @@ bool WriteState::emitRecord(NaClBitstreamWriter &Writer,
       if (!Flags.getTryToRecover())
         return false;
     }
+    if (atOutermostScope()) {
+      // Recover by ignoring abbreviation definition.
+      RecoverableError() << "Defining abbreviation outside block: "
+                         << Record << "\n";
+      return  Flags.getTryToRecover();
+    }
     NaClBitCodeAbbrev *Abbrev = buildAbbrev(Record);
     if (Abbrev == nullptr) {
       markCurrentBlockWithOmittedAbbreviations();