feat(loader, kernel): impl part of loader and initialize kernel structure

arch/x86_64/build_arch.zig

@@ -0,0 +1,26 @@
+const std = @import("std");
+const Step = std.Build.Step;
+const boot_build = @import("boot/build_boot.zig");
+
+fn buildKernel(b: *std.Build, optimize: std.builtin.OptimizeMode) *Step.Compile {
+    const target = b.resolveTargetQuery(.{
+        .cpu_arch = .x86_64,
+        .os_tag = .freestanding,
+        .abi = .none,
+    });
+    const kernel = b.addExecutable(.{
+        .name = "kernel",
+        .root_module = b.addModule("kernel", .{
+            .root_source_file = b.path("kernel/main.zig"),
+            .target = target,
+            .optimize = optimize,
+        }),
+    });
+    kernel.entry = .{ .symbol_name = "start_kernel" };
+    return kernel;
+}
+pub fn buildImage(b: *std.Build) void {
+    const optimize = b.standardOptimizeOption(.{});
+    const kernel = buildKernel(b, optimize);
+    boot_build.buildBootImage(b, kernel);
+}