Although "macOS" is the correct name for Apple's current desktop OS,
we've decided to go with "Mac OS" to cover all of Apple's Unix-like
desktop OS versions. The label "Mac OS" is more readable, clear in
context (i.e., unlikely to be confused with the Mac OSes that
proceeded Mac OS X), and as likely to match Apple's future OS names
as anything.
Expose tagged allocation and a function that interprets a description
of tagged shapes. As a furst cut, the description can only specify
constant offsets for pointers within the object, but future extensions
are possible.
To make the API consistent for MSVC versus MinGW builds, make
a functional formerly required for embedding on 32-bit Windows
always available and required for all Windows variants.
In the common case of a minor GC without a generation 1/2
or a major GC without compaction, a single pass suffices
to both mark and update references.
This change reduces overall GC time by 10%-25% on typical
programs.
