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

toolchain/compile_stub.sh

@@ -1,8 +1,15 @@
 #!/usr/bin/env bash
+# Multi-architecture build updates: Copyright 2026 Aaron Hance.
+set -e
+source "$(dirname "${BASH_SOURCE[0]}")/target.sh"
 echo " "
 echo "======================="
 echo " "
 echo "Compiling Stub..."
 echo " "
-nasm -f elf src/arch/x86/boot/stub.asm -o lib/stub.o
-nasm -f elf src/boot/splash_tga.asm -o lib/splash_tga.o
+nasm -f "$NASM_FORMAT" "src/arch/$ASURO_ARCH/boot/stub.asm" -o "$OBJ_DIR/stub.o"
+if [ "$ASURO_ARCH" = x86 ]; then
+    nasm -f "$NASM_FORMAT" src/boot/splash_tga.asm -o "$OBJ_DIR/splash_tga.o"
+else
+    nasm -f "$NASM_FORMAT" src/arch/x86_64/isr/entry.asm -o "$OBJ_DIR/isr_entry.o"
+fi