[cherry-pick release/6.0][Sema] Don't clear ParsedUnrecognizedPlatformName when a recognized platform is parsed

The callers of parsePlatformVersionInList need to know if an unrecognized platform was parsed in the whole list. It can get cleared in the case of (unrecognized 1.0, *) but PlatformAndVersions will still be empty.

rdar://134207783

Author: ian-twilightcoder

lib/Parse/ParseDecl.cpp

@@ -2226,7 +2226,7 @@ ParserStatus Parser::parsePlatformVersionInList(StringRef AttrName,
   // Parse the platform name.
   StringRef platformText = Tok.getText();
   auto MaybePlatform = platformFromString(platformText);
-  ParsedUnrecognizedPlatformName = !MaybePlatform.has_value();
+  ParsedUnrecognizedPlatformName = ParsedUnrecognizedPlatformName || !MaybePlatform.has_value();
   SourceLoc PlatformLoc = Tok.getLoc();
   consumeToken();