dwarf2out.c: fix jit issue with early_dwarf_finished

dwarf2out.c: fix jit issue with early_dwarf_finished

All of the jit testcases that generate debuginfo appear to have been
failing since r240228 on their 2nd in-process iteration on this
assertion in set_early_dwarf's ctor:

      gcc_assert (! early_dwarf_finished);

Root cause is that the global is never reset at the end of compilation,
which this patch fixes in the obvious way.

gcc/ChangeLog:
	* dwarf2out.c (dwarf2out_c_finalize): Reset early_dwarf and
	early_dwarf_finished.

From-SVN: r243136