Avoid cycles in Symbol toString under -Ydebug

This is the first of two commits to restore workingness
to the compiler under `-Ydebug`.

`ResetAttrs` is now called during case class unapply synthesis,
after the UnTyper was recently banished.

But, this class has some low-level tracing that is triggered
under `-Ydebug` (irrespective of any `-Ylog` settings.)

This tracing code calls `Symbol#toString`, which, in an attempt
to discriminate primary from secondary constructors, accesses
the info of its owner. This is sufficient to hit a dreaded
`CyclicReferenceError`.

The enclosed test compiles a case class under this option
to show that things now compile. It still spews out unwanted
output; this will be removed in the next commit.

1 files changed, 1 insertions, 0 deletions

diff --git a/test/files/pos/debug-reset-local-attrs.flags b/test/files/pos/debug-reset-local-attrs.flags
new file mode 100644
index 0000000000..9c7d6400fc
--- /dev/null
+++ b/test/files/pos/debug-reset-local-attrs.flags
@@ -0,0 +1 @@
+-Ydebug