gfx/common/vulkan: force MVK_CONFIG_USE_MTLHEAP=0 on Apple to avoid placement-heap crash

MoltenVK 1.3.0 flipped MVK_CONFIG_USE_MTLHEAP to active by default for
non-AMD GPUs, routing VkDeviceMemory through a placement MTLHeap.
Placement heaps need macOS 13+ AND supportsPlacementHeaps; older Intel
Macs satisfy neither and abort at swapchain-image allocation:

  -[MTLHeapDescriptorInternal validateWithDevice:]:335:
    failed assertion `Placement heap type is not supported.'

Force the path off in vulkan_context_init() before the loader is
opened, while still respecting an explicit user override. "0" is
boolean-false on 1.2.x and MVK_CONFIG_USE_MTLHEAP_NEVER on 1.3.x, so
the fix is version-agnostic.

Fixes #18985.

Author: LibretroAdmin

gfx/common/vulkan_common.c

@@ -2498,6 +2498,20 @@ bool vulkan_context_init(gfx_ctx_vulkan_data_t *vk,
          int use_mab                      = settings->bools.video_use_metal_arg_buffers;
          setenv("MVK_CONFIG_USE_METAL_ARGUMENT_BUFFERS", use_mab ? "1" : "0", 1);
       }
+      /* MoltenVK 1.3.0 flipped MVK_CONFIG_USE_MTLHEAP to active by default
+       * for all non-AMD GPUs, so VkDeviceMemory now allocates from a
+       * placement MTLHeap.  Placement heaps require macOS 13+ and a GPU
+       * that reports supportsPlacementHeaps; older Intel Macs (Mac GPU
+       * family 2 on macOS 12 and earlier) abort at swapchain-image
+       * allocation time with:
+       *   -[MTLHeapDescriptorInternal validateWithDevice:]:
+       *     failed assertion `Placement heap type is not supported.'
+       * Force the path off here so the assertion can never fire.  The
+       * value "0" is interpreted as boolean-false by 1.2.x and as the
+       * MVK_CONFIG_USE_MTLHEAP_NEVER enum value by 1.3.x, so it is
+       * forward- and backward-compatible.  See libretro/RetroArch#18985. */
+      if (!getenv("MVK_CONFIG_USE_MTLHEAP"))
+         setenv("MVK_CONFIG_USE_MTLHEAP", "0", 1);
       /* Try Vulkan loader first (enables validation layers if installed).
        * Falls back to MoltenVK directly if loader not available. */
       vulkan_library = dylib_load("libvulkan.dylib");