Serialization: restrict swiftmodules to distribution channels

There are scenarios where different compilers are distributed with
compatible serialization format versions and the same tag. Distinguish
swiftmodules in such a case by assigning them to different distribution
channels. A compiler expecting a specific channel will only read
swiftmodules from the same channel. The channels should be defined by
downstream code as it is by definition vendor specific.

For development, a no-channel compiler loads or defining the env var
SWIFT_IGNORE_SWIFTMODULE_REVISION skips this new check.

rdar://123731777

lib/Serialization/SerializedModuleLoader.cpp

@@ -1081,6 +1081,12 @@ void swift::serialization::diagnoseSerializedASTLoadFailure(
     Ctx.Diags.diagnose(diagLoc, diag::serialization_module_incompatible_revision,
                        loadInfo.problematicRevision, ModuleName, moduleBufferID);
     break;
+  case serialization::Status::ChannelIncompatible:
+    Ctx.Diags.diagnose(diagLoc, diag::serialization_module_incompatible_channel,
+                       loadInfo.problematicChannel,
+                       version::getCurrentCompilerChannel(),
+                       ModuleName, moduleBufferID);
+    break;
   case serialization::Status::Malformed:
     Ctx.Diags.diagnose(diagLoc, diag::serialization_malformed_module,
                        moduleBufferID);
@@ -1168,6 +1174,7 @@ void swift::serialization::diagnoseSerializedASTLoadFailureTransitive(
   case serialization::Status::NotInOSSA:
   case serialization::Status::NoncopyableGenericsMismatch:
   case serialization::Status::RevisionIncompatible:
+  case serialization::Status::ChannelIncompatible:
   case serialization::Status::Malformed:
   case serialization::Status::MalformedDocumentation:
   case serialization::Status::FailedToLoadBridgingHeader: