deleted two tests intended to test RUST_CC_ZEAL, an apparently defunct flag for the cycle collector
remove (non-parsing) test related to impl d for d feature
this issue is a dup of another one that has a correct test case

this test case has rotted wrt modern syntax. fortunately, this issue
was a dup of another one, and that one still ICEs.
This test case is obsolete for two reasons

First, it refers to a feature (trait bounds on type parameters) that's
apparently no longer in the language. Second, if I understand the issue
correctly, it should never have been a "run-pass" test because it was
supposed to fail.
changed to impl trait for type stx
Got test cases to pass, after some major surgery
this test still doesn't pass, but at least it parses...
This test case now parses

I've done a slapdash job of fixing up the syntax; it didn't pass before,
and it doesn't pass now, but at least it parses...
Test now passes
added test case for issue 5927
with syntax fixes, this test case now appears to pass
fixed up test, but now it has a trait failure
looks like we don't support overlapping traits like this any more
after syntax fixes, these tests appear to pass