fix(aot): reserve x18 register on macOS ARM64

Apple reserves CPU register x18 for TLS on ARM64. When generating AOT
code for aarch64 on macOS, LLVM may use x18, causing crashes when the
AOT code runs on macOS ARM64 (M1/M2/M3).

This patch:
1. Detects darwin/macho ABI and sets correct vendor string
2. Detects darwin/apple in default triple for platform detection
3. Adds +reserve-x18 to LLVM target features for aarch64 on macOS

The fix only applies when compiling on macOS ARM64 hosts, ensuring
generated AOT code is compatible with Apple's platform requirements.

Author: teamchong

core/iwasm/compilation/aot_llvm.c

@@ -3005,6 +3005,10 @@ aot_create_comp_context(const AOTCompData *comp_data, aot_comp_option_t option)
                 else
                     vendor_sys = "-pc-windows-";
             }
+            else if (!strcmp(abi, "darwin") || !strcmp(abi, "macho")) {
+                /* macOS/Darwin: x18 is reserved by Apple */
+                vendor_sys = "-apple-";
+            }
             else {
                 if (is_baremetal_target(arch, cpu, abi))
                     vendor_sys = "-unknown-none-";
@@ -3050,6 +3054,14 @@ aot_create_comp_context(const AOTCompData *comp_data, aot_comp_option_t option)
                 if (!abi)
                     abi = "gnu";
             }
+            else if (strstr(default_triple, "darwin")
+                     || strstr(default_triple, "apple")) {
+                /* macOS/Darwin: x18 is reserved by Apple, must use correct
+                 * triple to prevent LLVM from using it */
+                vendor_sys = "-apple-darwin";
+                if (!abi)
+                    abi = "";
+            }
             else {
                 vendor_sys = "-pc-linux-";
                 if (!abi)
@@ -3139,6 +3151,30 @@ aot_create_comp_context(const AOTCompData *comp_data, aot_comp_option_t option)
         if (!features)
             features = "";
 
+#if (defined(__APPLE__) || defined(__MACH__)) && defined(BUILD_TARGET_AARCH64)
+        /* On macOS ARM64, x18 is reserved by Apple for TLS. Even though we're
+         * generating ELF (Linux-style) AOT files, we must tell LLVM to not
+         * use x18, otherwise the AOT code will crash when running on macOS. */
+        {
+            bool is_aarch64 = false;
+            if (arch && !strncmp(arch, "aarch64", 7))
+                is_aarch64 = true;
+            else if (triple_norm && strstr(triple_norm, "aarch64"))
+                is_aarch64 = true;
+
+            if (is_aarch64) {
+                if (features[0] != '\0') {
+                    snprintf(features_buf, sizeof(features_buf), "%s,+reserve-x18",
+                             features);
+                    features = features_buf;
+                }
+                else {
+                    features = "+reserve-x18";
+                }
+            }
+        }
+#endif
+
         /* Get target with triple, note that LLVMGetTargetFromTriple()
            return 0 when success, but not true. */
         if (LLVMGetTargetFromTriple(triple_norm, &target, &err) != 0) {