Parsing is the easy part of a C++ compiler, and the T t example you mentioned has a relatively simple solution (which is, as you say, using the symbol table). In fact that ambiguity is present in C as well (with typedefs), and yet it hasn't really stopped many others from writing their own C compilers which handle that case.

It's the things like templates, multiple/virtual inheritance, and argument-dependent lookup/overload resolution which are difficult to get right, and the reason that even somewhat fully-featured C++ compilers are rare.