[ruby-core:64879] Re: [ruby-trunk - Bug #10206] [Open] garbage symbols crash symbol GC

I'm looking into uses of intern_cstr_without_pindown in parse.y causing
garbage syms.

Unfortunately, I do not yet understand why we avoid pindown in parse.y
(or much of parse.y).  I thought symbol GC was only to help users who
use String#to_sym too aggressively.

> 	http://80x24.org/r35240/gdb-bt.txt

compile.c:
		      case TS_ID: /* ID */
			generated_iseq[pos + 1 + j] = SYM2ID(operands[j]);