Parse tree misinterprets typedefs as function definitions when using extension keyword

[nikitam95]

When parsing C code that uses the __extension__ keyword, the parse tree generated by Tree-sitter C language incorrectly treat typedef declarations as function definitions.

To Reproduce
Parse the following C code:

__extension__ typedef struct {  
  long long int quot;  
  long long int rem;  
} lldiv_t;  

Expected behavior
The parse tree should correctly recognize that this is a typedef declaration and not a function definition.

[Amaan Qureshi]

It's a gnu extension that we don't have added atm (__extension__ that is), feel free to PR support for it or I can in a bit