Figure out what the fixed expression is, and print it. Added another target setting to

quietly apply fixits for those who really trust clang's fixits.

Also, moved the retry into ClangUserExpression::Evaluate, where I can make a whole new ClangUserExpression 
to do the work.  Reusing any of the parts of a UserExpression in situ isn't supported at present.

<rdar://problem/25351938>

llvm-svn: 264793