PR34163: Don't cache an incorrect key function for a class if queried between

the class becoming complete and its inline methods being parsed.

This replaces the hack of using the "late parsed template" flag to track member
functions with bodies we've not parsed yet; instead we now use the "will have
body" flag, which carries the desired implication that the function declaration
*is* a definition, and that we've just not parsed its body yet.

llvm-svn: 310776