swift234

Nuke entry-point-based process args

Provides a new fallback for Process arguments for those instances where we do
not own main (e.g. Frameworks, Objective-C owns main.m or main.c, etc.). This
includes a number of platform-specific specializations of argument grabbing
logic and a new thread-safe interface to Process.unsafeArgv.

main()  | _NSGetArgc/_NSGetArgv    | /proc/self/cmdline     | __argc/__argv
--------|--------------------------|------------------------|---------------
Scripts | OS X, iOS, tvOS, watchOS | Linux, FreeBSD, Cygwin | Windows

For interpreted Swift where we must filter out the arguments we now do so by
loading the standard library and calling into new SPI to override the arguments
that would have been grabbed by the runtime. This implementation completely
subsumes the use of the entry point  '_stdlib_didEnterMain' and it will be
removed in a future commit.