[CodeView] Handle Cross Module Imports and Exports.

While it's not entirely clear why a compiler or linker might
put this information into an object or PDB file, one has been
spotted in the wild which was causing llvm-pdbdump to crash.

This patch adds support for reading-writing these sections.
Since I don't know how to get one of the native tools to
generate this kind of debug info, the only test here is one
in which we feed YAML into the tool to produce a PDB and
then spit out YAML from the resulting PDB and make sure that
it matches.

llvm-svn: 304738
diff --git a/llvm/lib/DebugInfo/CodeView/CMakeLists.txt b/llvm/lib/DebugInfo/CodeView/CMakeLists.txt
index 410b89b..c543a6e 100644
--- a/llvm/lib/DebugInfo/CodeView/CMakeLists.txt
+++ b/llvm/lib/DebugInfo/CodeView/CMakeLists.txt
@@ -3,11 +3,9 @@
   CodeViewRecordIO.cpp
   CVSymbolVisitor.cpp
   CVTypeVisitor.cpp
-  EnumTables.cpp
-  Formatters.cpp
-  LazyRandomTypeCollection.cpp
-  Line.cpp
   DebugChecksumsSubsection.cpp
+  DebugCrossExSubsection.cpp
+  DebugCrossImpSubsection.cpp
   DebugFrameDataSubsection.cpp
   DebugInlineeLinesSubsection.cpp
   DebugLinesSubsection.cpp
@@ -16,6 +14,10 @@
   DebugSubsectionRecord.cpp
   DebugSubsectionVisitor.cpp
   DebugSymbolsSubsection.cpp
+  EnumTables.cpp
+  Formatters.cpp
+  LazyRandomTypeCollection.cpp
+  Line.cpp
   RecordSerialization.cpp
   SymbolRecordMapping.cpp
   SymbolDumper.cpp