MS ABI: Document the '\xc1' to '\xda' manglings

No functionality change.

llvm-svn: 205223

clang/lib/AST/MicrosoftMangle.cpp

@@ -2419,6 +2419,7 @@ void MicrosoftMangleContextImpl::mangleStringLiteral(const StringLiteral *SL,
       Mangler.getStream() << Byte;
     } else if ((Byte >= '\xe1' && Byte <= '\xfa') ||
                (Byte >= '\xc1' && Byte <= '\xda')) {
+      // The delta between '\xe1' and '\xc1' is the same as 'a' to 'A'.
       Mangler.getStream() << '?' << static_cast<char>('A' + (Byte - '\xc1'));
     } else {
       switch (Byte) {