Rename C++ macro 'defer' -> 'SWIFT_DEFER'

In C++ we can't have nice things. The macro name 'defer' collided with
use of 'defer' in the Tokens.def file and we were already doing horrible
workarounds in a couple of places to allow them to be included into the
same file. So use a less awesome but more robust name (thanks to Joe for
suggesting SWIFT_DEFER).

Incidentally, sort a bunch of #inlcudes.

lib/Parse/ParseDecl.cpp

@@ -4073,7 +4073,7 @@ ParserStatus Parser::parseDeclVar(ParseDeclOptions Flags,
 
   // No matter what error path we take, make sure the
   // PatternBindingDecl/TopLevel code block are added.
-  defer {
+  SWIFT_DEFER {
     // If we didn't parse any patterns, don't create the pattern binding decl.
     if (PBDEntries.empty())
       return;