-DBOOST_COBALT_NO_PMR=1 breaks MSVC build

[francoisk]

The MSVC build fails with the following error if -DBOOST_COBALT_NO_PMR=1 is defined:

src\detail\util.cpp(23): error C2039: 'get_allocator': is not a member of 'boost::cobalt::this_thread'
src\detail\util.cpp(23): error C3861: 'get_allocator': identifier not found

As can be seen in the code snippets below, boost::cobalt::this_thread::get_allocator() is not declared if BOOST_COBALT_NO_PMR is defined, yet it is called unconditionally under MSVC.

cobalt/include/boost/cobalt/this_thread.hpp

Lines 20 to 24 in af72ced

	#if !defined(BOOST_COBALT_NO_PMR)
	BOOST_COBALT_DECL pmr::memory_resource* get_default_resource() noexcept;
	BOOST_COBALT_DECL pmr::memory_resource* set_default_resource(pmr::memory_resource* r) noexcept;
	BOOST_COBALT_DECL pmr::polymorphic_allocator<void> get_allocator();
	#endif

cobalt/include/boost/cobalt/config.hpp

Lines 29 to 32 in af72ced

	#if defined(_MSC_VER)
	// msvc doesn't correctly suspend for self-deletion, hence we must workaround here
	#define BOOST_COBALT_NO_SELF_DELETE 1
	#endif

cobalt/src/detail/util.cpp

Lines 17 to 28 in af72ced

	#if BOOST_COBALT_NO_SELF_DELETE
	void self_destroy(std::coroutine_handle<void> h, const cobalt::executor & exec) noexcept
	{
	asio::post(exec,
	asio::bind_allocator(
	this_thread::get_allocator(),
	[del=unique_handle<void>(h.address())]() mutable
	{
	}));
	}
	#endif