Redundant typedef causes m2c to hang

[r-burns]

I was having trouble decompiling on m2c using an autogenerated context header, which was causing the decompilation step to hang indefinitely. I was able to trim my context down to this minimal reproducer:

typedef int foo;
typedef foo foo;
struct bar {
    foo x;
};

I initially thought this was malformed code, but mwcc and GCC will happily compile it -- either way, I think m2c shouldn't hang on this. It seems like it's getting stuck while building the typemap.