libphobos: Add section support code for MACHO and PE/COFF

libphobos: Add section support code for MACHO and PE/COFF

This replaces the original and untested support for Windows and OSX, and
is the 90% of the work needed to support libphobos on those targets.

The core.thread interface has been updated to accomodate for the same
function might be implemented by any of the platform-dependent modules.

libphobos/ChangeLog:

	* libdruntime/Makefile.am (DRUNTIME_DSOURCES): Removed
	gcc/sections/android.d, elf_shared.d, osx.d, win32.d, and win64.d.
	Added gcc/sections/common.d, elf.d macho.d, and pecoff.d.
	* libdruntime/Makefile.in: Regenerate.
	* libdruntime/core/thread/osthread.d: Update externDFunc FQDN names to
	use platform independant section function names.
	* libdruntime/gcc/sections/elf_shared.d: Renamed to...
	* libdruntime/gcc/sections/elf.d: ...this.  Mangle functions for
	core.thread interface as if they come from the gcc.sections module.
	* libdruntime/gcc/sections/package.d: Update public imports, declare
	functions for core.thread interface.
	* libdruntime/gcc/sections/android.d: Removed.
	* libdruntime/gcc/sections/osx.d: Removed.
	* libdruntime/gcc/sections/win32.d: Removed.
	* libdruntime/gcc/sections/win64.d: Removed.
	* libdruntime/gcc/sections/common.d: New file.
	* libdruntime/gcc/sections/macho.d: New file.
	* libdruntime/gcc/sections/pecoff.d: New file.