Add x86_64 kernel bring-up with build-selected platform adapters

toolchain/target.sh

@@ -0,0 +1,36 @@
+#!/usr/bin/env bash
+# Copyright 2026 Aaron Hance
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+# http://www.apache.org/licenses/LICENSE-2.0
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+# Shared target selection. Source this file from build steps.
+ASURO_ARCH="${ASURO_ARCH:-x86}"
+case "$ASURO_ARCH" in
+    x86)
+        OBJ_DIR=lib
+        BIN_DIR=bin
+        ISO_ROOT=iso
+        ISO_FILE=Asuro.iso
+        NASM_FORMAT=elf
+        LD_FORMAT=elf_i386
+        LINKER_SCRIPT=toolchain/linker.script
+        ;;
+    x86_64)
+        OBJ_DIR=lib/x86_64
+        BIN_DIR=bin/x86_64
+        ISO_ROOT=bin/x86_64/iso
+        ISO_FILE=Asuro-x86_64.iso
+        NASM_FORMAT=elf64
+        LD_FORMAT=elf_x86_64
+        LINKER_SCRIPT=toolchain/x86_64/linker.script
+        ;;
+    *) echo "Unsupported ASURO_ARCH: $ASURO_ARCH" >&2; exit 1 ;;
+esac
+export ASURO_ARCH OBJ_DIR BIN_DIR ISO_ROOT ISO_FILE NASM_FORMAT LD_FORMAT LINKER_SCRIPT