[Serialization] Use a more reliable macro to get the compiler tag

Use only the SWIFT_COMPILER_VERSION macro to check for swiftmodules
being written by the same compiler that reads it. In practice, it's the
macro used for release builds of the compiler.

rdar://96868333

lib/Serialization/Serialization.cpp

@@ -1004,7 +1004,7 @@ void Serializer::writeHeader(const SerializationOptions &options) {
     static const char* forcedDebugRevision =
       ::getenv("SWIFT_DEBUG_FORCE_SWIFTMODULE_REVISION");
     auto revision = forcedDebugRevision ?
-      forcedDebugRevision : version::getSwiftRevision();
+      forcedDebugRevision : version::getCurrentCompilerTag();
     Revision.emit(ScratchRecord, revision);
 
     IsOSSA.emit(ScratchRecord, options.IsOSSA);