[Serialization] Keep track of whether a module has an underlying Clang module.

Previously, we depended on whether or not a serialized module was located
within a framework bundle to consider whether or not it may have a "Clang
half". However, LLDB loads serialized modules from dSYM bundles. Rather
than try to figure out if such a module is "really" a framework, just track
whether the original module was built with -import-underlying-module. If so,
consider the underlying Clang module to be re-exported.

rdar://problem/18099523

Swift SVN r21544

include/swift/Serialization/ModuleFormat.h

@@ -40,7 +40,7 @@ const uint16_t VERSION_MAJOR = 0;
 /// Serialized module format minor version number.
 ///
 /// When the format changes IN ANY WAY, this number should be incremented.
-const uint16_t VERSION_MINOR = 130;
+const uint16_t VERSION_MINOR = 131;
 
 using DeclID = Fixnum<31>;
 using DeclIDField = BCFixed<31>;
@@ -355,6 +355,7 @@ namespace input_block {
     LINK_LIBRARY,
     IMPORTED_HEADER,
     IMPORTED_HEADER_CONTENTS,
+    MODULE_FLAGS
   };
 
   using SourceFileLayout = BCRecordLayout<
@@ -390,6 +391,11 @@ namespace input_block {
     IMPORTED_HEADER_CONTENTS,
     BCBlob
   >;
+
+  using ModuleFlagsLayout = BCRecordLayout<
+    MODULE_FLAGS,
+    BCFixed<1> // has underlying module?
+  >;
 }
 
 /// The record types within the "decls-and-types" block.