mac: disable bf16 on unsupported OS versions (#11585)

Support for bf16 was added in MacOS v14+ and attempting to enable
on older versions causes runtime failures.

llama/patches/0019-metal-add-mean-kernel-14267.patch

@@ -19,7 +19,7 @@ diff --git a/ggml/src/ggml-metal/ggml-metal.m b/ggml/src/ggml-metal/ggml-metal.m
 index a9eeebc6..110c9ece 100644
 --- a/ggml/src/ggml-metal/ggml-metal.m
 +++ b/ggml/src/ggml-metal/ggml-metal.m
-@@ -489,6 +489,7 @@ enum ggml_metal_kernel_type {
+@@ -489,6 +489,7 @@ static void ggml_backend_metal_device_rel(struct ggml_backend_metal_device_conte
      GGML_METAL_KERNEL_TYPE_COS,
      GGML_METAL_KERNEL_TYPE_NEG,
      GGML_METAL_KERNEL_TYPE_SUM_ROWS,
@@ -27,7 +27,7 @@ index a9eeebc6..110c9ece 100644
      GGML_METAL_KERNEL_TYPE_POOL_2D_AVG_F32,
      GGML_METAL_KERNEL_TYPE_POOL_2D_MAX_F32,
      GGML_METAL_KERNEL_TYPE_ARGMAX,
-@@ -1436,6 +1437,7 @@ static struct ggml_backend_metal_context * ggml_metal_init(ggml_backend_dev_t de
+@@ -1436,6 +1437,7 @@ @implementation GGMLMetalClass
          GGML_METAL_ADD_KERNEL(GGML_METAL_KERNEL_TYPE_COS,                             cos,                             true);
          GGML_METAL_ADD_KERNEL(GGML_METAL_KERNEL_TYPE_NEG,                             neg,                             true);
          GGML_METAL_ADD_KERNEL(GGML_METAL_KERNEL_TYPE_SUM_ROWS,                        sum_rows,                        true);

llama/patches/0022-BF16-macos-version-guard.patch

+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: Daniel Hiltgen <daniel@ollama.com>
+Date: Wed, 30 Jul 2025 08:43:46 -0700
+Subject: [PATCH] BF16 macos version guard
+
+Only enable BF16 on supported MacOS versions (v14+)
+---
+ ggml/src/ggml-metal/ggml-metal.m | 6 +++++-
+ 1 file changed, 5 insertions(+), 1 deletion(-)
+
+diff --git a/ggml/src/ggml-metal/ggml-metal.m b/ggml/src/ggml-metal/ggml-metal.m
+index 110c9ece..ab46f6e3 100644
+--- a/ggml/src/ggml-metal/ggml-metal.m
++++ b/ggml/src/ggml-metal/ggml-metal.m
+@@ -89,7 +89,11 @@
+         ctx->has_bfloat |= [ctx->mtl_device supportsFamily:MTLGPUFamilyApple6];
+ 
+ #if defined(GGML_METAL_USE_BF16)
+-        ctx->use_bfloat = ctx->has_bfloat;
++        if (@available(macOS 14.0, *)) {
++            ctx->use_bfloat = ctx->has_bfloat;
++        } else {
++            ctx->use_bfloat = false;
++        }
+ #else
+         ctx->use_bfloat = false;
+ #endif

ml/backend/ggml/ggml/src/ggml-metal/ggml-metal.m

@@ -89,7 +89,11 @@ static id<MTLDevice> ggml_backend_metal_device_acq(struct ggml_backend_metal_dev
         ctx->has_bfloat |= [ctx->mtl_device supportsFamily:MTLGPUFamilyApple6];
 
 #if defined(GGML_METAL_USE_BF16)
-        ctx->use_bfloat = ctx->has_bfloat;
+        if (@available(macOS 14.0, *)) {
+            ctx->use_bfloat = ctx->has_bfloat;
+        } else {
+            ctx->use_bfloat = false;
+        }
 #else
         ctx->use_bfloat = false;
 #endif