Suppress a libuv leak on mac

I suspect that this is a race between process exit and the termination of
worker threads used by libuv (if I sleep before exit it doesn't leak). This
isn't going to cause any real problems but should probably be fixed at
some point.
register snapshots
remove obsolete `foreach` keyword

this has been replaced by `for`
rm obsolete `for` support from the compiler
auto merge of #8264 : thestinger/rust/snapshot, r=Aatch
rt: Fix a corner-case in unwinding that leads to stack overflow

In some scenarios upcall_rust_stack_limit fails to record the stack
limit, leaving it 0, and allowing subsequent Rust code to run into
the red zone.
auto merge of #8217 : brson/rust/reset_stack_limit, r=pcwalton

In some scenarios upcall_rust_stack_limit fails to record the stack
limit, leaving it 0, and allowing subsequent Rust code to run into
the red zone.
auto merge of #8254 : brson/rust/libuv-mac-supp, r=pcwalton

I suspect that this is a race between process exit and the termination of
worker threads used by libuv (if I sleep before exit it doesn't leak). This
isn't going to cause any real problems but should probably be fixed at
some point.

r? @pcwalton

cc #8253