Type name and variable name conflicts cause stack overflow

[clkbug]

Hi.
veryl check/build command agiainst the following code causes fatal runtime error: stack overflow

module mod (
    x: input x,
) {
}

This may not be a problem in practical terms, but I was a bit surprised when I mistyped clk: input clk.

[nblei]

@dalance The stack overflow is caused by unbounded recurssion in the symbol table's resolve function.

(resolve -> trace_user_defined ->)*