macOS (Apple Silicon) support: native build running under Rosetta 2 with MoltenVK (#102)

* macos: POSIX platform layer (host fault handler, virtual memory)

- hostException: Mach/POSIX signal-based host fault handler mirroring the
  Windows vectored handler (SIGSEGV/SIGBUS/SIGILL), behind
  '#elif defined(__APPLE__)'. Windows and Linux branches are untouched.
- sysLinuxVirtual: mach_vm_region-based is_mapped (no /proc/self/maps on
  macOS), PTHREAD_MUTEX_NORMAL, and a MAP_FIXED carve-in-place allocator that
  never leaves an unmapped hole for dyld/Rosetta/Metal to claim. All
  __APPLE__-guarded; the original Linux allocator path is preserved verbatim.
- sysLinuxDbg/sysLinuxFileIO: libgen.h for basename(), and a POSIX
  opendir/readdir implementation of SysFileGetDents (previously a stub).

* macos: guest kernel backing, threads, and POSIX libs

- memory/memoryAddressSpace: anonymous shm_open backing (macOS has no
  memfd_create) and re-reserve-on-unmap so a guest MAP_FIXED remap never
  destroys a host mapping (__APPLE__-guarded). Drops host <sys/mman.h> MAP_*
  macros so the guest's constexpr MAP_* constants compile (no-op on Windows).
- pthread: undef the host PTHREAD_STACK_MIN macro; on non-Windows, pin the
  stack-switch asm's guest rsp/rbp to callee-saved r14/r15 (the template
  clobbers r12/r13); __APPLE__ no-op for the absent pthread_condattr_setclock.
  The Windows stack-switch asm is byte-identical.
- network: define SOCKET/INVALID_SOCKET for the non-Windows paths (were
  undefined at 20+ use sites), and rename the non-Windows kernel_clock_*
  helpers to the CamelCase names the callers already use. Both repair the
  shared non-Windows build. Integer reinterpret_cast -> static_cast.

* loader: pin stack-switch asm operands to callee-saved registers

RunEntry switches to the guest stack with an asm template that clobbers
r12/r13 before consuming its inputs. With plain "r" constraints the compiler
may place func/guest_rsp/guest_rbp into r12/r13, so 'callq *func' jumps
through the saved host rsp -- a latent miscompile on every platform that any
unrelated codegen change can trigger. Pin the inputs to rbx/r14/r15, which the
template never touches and the SysV callee preserves.

General correctness fix (not macOS-specific); the same fix is applied to
pthread RunOnGuestStack.

* macos: Vulkan/MoltenVK graphics enablement

- pageManager: GPU write-tracking via Mach VM queries + mprotect (mprotect
  cannot report the previous protection, so the expected-old check is dropped),
  thread id via pthread_mach_thread_np, 4 KB page-size check -- __APPLE__-guarded.
- shaders/renderDraw/vulkanWindow: MoltenVK lacks VK_EXT_color_write_enable,
  VK_EXT_depth_clip_enable and depthBounds; fall back to static color-write
  masks and default depth clipping, request VK_KHR_portability_subset, and
  reuse the graphics queue for present when only one queue is exposed. Non-Apple
  pipeline/extension setup is unchanged.
- window: optional borderless window (KYTY_BORDERLESS) to sidestep a Rosetta
  NSException in macOS window chrome.

* graphics: macOS thread identity for region tracking

Region-ownership locks resolve the current thread via GetCurrentThreadId()
on Windows and EXIT elsewhere. Use the Mach thread port on macOS (nonzero
per-thread id; 0 stays the no-owner sentinel).

* macos: marshal AppKit window operations to the main thread

The present worker thread shows the window, updates its icon and title, and
recreates a lost Vulkan surface. AppKit traps with 'Must only be used from the
main thread' when these run off the main thread. Route them through a small
task queue drained by the SDL main loop (an SDL_USEREVENT wakes the loop when
it is blocked in SDL_WaitEvent). Title updates are fire-and-forget; showing
the window and surface recreation wait for completion.

Windows and Linux call the SDL functions directly, as before.

* build: ignore the _Build output directory

_Build is the conventional out-of-tree build location (only _Build/vscode-clang
was ignored); a stray git add could sweep build artifacts into a commit.

* macos: isolate stack-switch workaround

---------

Co-authored-by: nmzik <Nmzik@mail.ru>

src/kernel/memoryAddressSpace.inc

@@ -191,9 +191,15 @@ public:
 			SetFailure(failure_reason, FailureReason::ReserveAlignedFailed);
 			return 0;
 		}
+#if !defined(__APPLE__)
+		// On macOS the PROT_NONE reservation is left in place: MapView's MAP_FIXED
+		// replaces it atomically, so the range never becomes a hole that dyld,
+		// Rosetta, or Metal background threads could claim (which the subsequent
+		// MAP_FIXED would then silently destroy).
 		if (!ReleaseReservedProbe(reserved, failure_reason)) {
 			return 0;
 		}
+#endif
 		if (MapFixed(reserved, size, backing_offset, mode, failure_reason)) {
 			return reserved;
 		}
@@ -1061,7 +1067,17 @@ private:
 		return ptr;
 	}
 
-	static bool UnmapView(void* vaddr, uint64_t size) { return munmap(vaddr, size) == 0; }
+	static bool UnmapView(void* vaddr, uint64_t size) {
+#if defined(__APPLE__)
+		// Re-reserve instead of freeing: the guest may MAP_FIXED-remap this range
+		// later, and that must never destroy a host mapping (dyld, Rosetta, Metal)
+		// that moved into the hole in the meantime.
+		return mmap(vaddr, size, PROT_NONE, MAP_FIXED | MAP_PRIVATE | MAP_ANON | MAP_NORESERVE,
+		            -1, 0) != MAP_FAILED;
+#else
+		return munmap(vaddr, size) == 0;
+#endif
+	}
 
 	static bool UnmapViewPreservePlaceholder(void* /*vaddr*/, uint64_t /*size*/) { return false; }