(De-)serialization for foreign error conventions.

Currently untestable (due to SILGen's inability to handle throwing
@objc methods), but testing will become trivial once that's in place.

Swift SVN r27294

include/swift/Serialization/ModuleFormat.h

@@ -51,7 +51,7 @@ const uint16_t VERSION_MAJOR = 0;
 /// To ensure that two separate changes don't silently get merged into one
 /// in source control, you should also update the comment to briefly
 /// describe what change you made.
-const uint16_t VERSION_MINOR = 191; // Last change: consolidate function type representations
+const uint16_t VERSION_MINOR = 192; // Last change: foreign error convention
 
 using DeclID = Fixnum<31>;
 using DeclIDField = BCFixed<31>;
@@ -115,6 +115,15 @@ enum class FunctionTypeRepresentation : uint8_t {
 };
 using FunctionTypeRepresentationField = BCFixed<4>;
 
+enum class ForeignErrorConventionKind : uint8_t {
+  ZeroResult,
+  NonZeroResult,
+  NilResult,
+  NonNilError,
+};
+
+using ForeignErrorConventionKindField = BCFixed<2>;
+
 // These IDs must \em not be renumbered or reordered without incrementing
 // VERSION_MAJOR.
 enum class SILFunctionTypeRepresentation : uint8_t {
@@ -1200,6 +1209,15 @@ namespace decls_block {
     BCFixed<1> // is a decl
   >;
 
+  using ForeignErrorConventionLayout = BCRecordLayout<
+    FOREIGN_ERROR_CONVENTION,
+    ForeignErrorConventionKindField,  // kind
+    BCFixed<1>,                       // owned
+    BCVBR<4>,                         // error parameter index
+    TypeIDField,                      // error parameter type
+    TypeIDField                       // result type
+  >;
+
   using AbstractClosureExprLayout = BCRecordLayout<
     ABSTRACT_CLOSURE_EXPR_CONTEXT,
     TypeIDField, // type