Changed the SymbolFile::FindFunction() function calls to only return

lldb_private::Function objects. Previously the SymbolFileSymtab subclass
would return lldb_private::Symbol objects when it was asked to find functions.

The Module::FindFunctions (...) now take a boolean "bool include_symbols" so
that the module can track down functions and symbols, yet functions are found
by the SymbolFile plug-ins (through the SymbolVendor class), and symbols are
gotten through the ObjectFile plug-ins.

Fixed and issue where the DWARF parser might run into incomplete class member
function defintions which would make clang mad when we tried to make certain
member functions with invalid number of parameters (such as an operator=
operator that had no parameters). Now we just avoid and don't complete these
incomplete functions.

llvm-svn: 124359