libphobos: Add Thread/Fiber support code for Darwin (PR98058)

libphobos/ChangeLog:

	PR d/98058
	* configure: Regenerate.
	* libdruntime/Makefile.am (DRUNTIME_DSOURCES_DARWIN): Add
	core/sys/darwin/config.d
	* libdruntime/Makefile.in: Regenerate.
	* libdruntime/config/powerpc/switchcontext.S: Implement
	fiber_switchContext for __MACH__.
	* libdruntime/config/x86/switchcontext.S: Likewise.
	* libdruntime/core/sys/darwin/config.d: New file.
	* libdruntime/core/thread/fiber.d (Fiber.getThis): Mark noinline.
	(UnsafeFiberMigration): Define for OSX/X86 and OSX/X86_64.
	* libdruntime/core/thread/osthread.d (callWithStackShell): Add inline
	assembler implementation for X86, X86_64, PPC, and PPC64.
	* libdruntime/core/thread/threadbase.d (ThreadBase.getThis): Mark
	noinline.
	* libdruntime/gcc/deh.d (FuncTable): Remove definition.
	* m4/druntime/os.m4 (DRUNTIME_OS_MINFO_BRACKETING): Check for right
	bracket symbol on darwin* targets.
	* testsuite/libphobos.thread/fiber_guard_page.d: Update test to
	support ucontext-based Fibers.