libphobos: Add section support code for OpenBSD (PR99691)

libphobos/ChangeLog:

	PR d/99691
	* configure: Regenerate.
	* libdruntime/config/common/threadasm.S: Add __OpenBSD__.
	* libdruntime/gcc/backtrace.d: Import core.sys.openbsd.dlfcn on
	OpenBSD platforms.
	* libdruntime/gcc/sections/elf.d (SharedElf): Define on OpenBSD.
	(linkMapForHandle): Implement for OpenBSD.
	(exeLinkMap): Remove.
	(getDependencies): Adjust dlpi_addr on OpenBSD.
	(handleForName): Implement for OpenBSD.
	(IterateManually): Define on OpenBSD.
	* libdruntime/gcc/sections/package.d (SectionsElf): Define on OpenBSD.
	* m4/druntime/libraries.m4 (DRUNTIME_LIBRARIES_ATOMIC): Test for
	enable_libatomic.
	(DRUNTIME_LIBRARIES_BACKTRACE): Test for enable_libbacktrace.