Section scans (for metadata, protocols, etc.) can be costly. This change adds tracing calls to those scans so we can more easily see how much time is spent in these scans and where they're initiated.
This adds an os_signpost implementation controlled by SWIFT_STDLIB_TRACING, and a default empty implementation for when that's disabled.
rdar://110266743
Apply a blanket pass of including `new` for the placement new allocation
and namespacing the call to the global placement new allocator. This
should repair the Android ARMv7 builds.
