c2compiler: sub-struct initialization fails

The analysis pass of the following code fails:

type T struct {
    i32 i;
    union {
        u32 u;
        void* p;
    }
}

T t1 = { 10, .u=20 }     // error: field designator 'u' does not refer to any field in type '(struct)T'

Mixing designated initializers with non-designated ones seems to be allowed in C for substructs. The Analyzer also needs to search sub-structs/unions and keep track of what’s initialized as well