As a side effect, this reduces cygwin C testsuite passes by a bit over
700, because we are no longer torture testing the -gcoff.  This is not
a regression.

An interesting thing to notice here is that we are torture testing
dwarf-2, but are not torture testing any of the later dwarf
versions.  We don't need to torture test all of them, but we probably
should torture test the latest usable one, which is dwarf-4 at the
moment.  This is a separate issue though that I have not tried to fix
here.

Jim