ActOnPseudoDestructorExpr now performs all semantic analysis for

pseudo-destructor expressions, and builds the CXXPseudoDestructorExpr
node directly. Currently, this only affects pseudo-destructor
expressions when they are parsed, but not after template
instantiation. That's coming next...

Improve parsing of pseudo-destructor-names. When parsing the
nested-name-specifier and we hit the sequence of tokens X :: ~, query
the actual module to determine whether X is a type-name (in which case
the X :: is part of the pseudo-destructor-name but not the
nested-name-specifier) or not (in which case the X :: is part of the
nested-name-specifier). 

llvm-svn: 97058