swift234

CMake: Fix string escaping of compiler version so that it works with the Xcode generator.  Xcode did not like parsing strings with unbalanced quotes
in the plist file.

This was exposed by r15694, but probably did not manifest as
the string escaping logic previously only happened on B&I submissions.

In this approach, the final version quad is turned into a string
within Version.cpp, not at the -D invocation.

Swift SVN r15708