Avoid symbol lookup for field names in C parser

Avoid symbol lookup for field names in C parser

Currently, the C parser looks up any name it finds -- at lex time.
However, in an expression like "obj->field", looking up the field name
is wasteful, and can sometimes even yield pathological symtab
expansion behavior.

This patch arranges to avoid the name lookup in this case.  (It would
be nice to really clean up this area, but I'm not convinced it can
readily be done in a yacc parser.)

Some special code is required for the C++ construct where a qualified
name is used, like "obj->type1::type2::field".

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=33081