src/core: move mach-core@9a4d09707d9f1cb6ea5602bdf58caeefc46146be package to here

Helps hexops/mach#1165

Signed-off-by: Stephen Gutekanst <stephen@hexops.com>

src/core/platform/native_entrypoint.zig

@@ -0,0 +1,39 @@
+// Check that the user's app matches the required interface.
+comptime {
+    if (!@import("builtin").is_test) @import("mach").core.AppInterface(@import("app"));
+}
+
+// Forward "app" declarations into our namespace, such that @import("root").foo works as expected.
+pub usingnamespace @import("app");
+const App = @import("app").App;
+
+const std = @import("std");
+const core = @import("mach").core;
+
+pub usingnamespace if (!@hasDecl(App, "GPUInterface")) struct {
+    pub const GPUInterface = core.wgpu.dawn.Interface;
+} else struct {};
+
+pub usingnamespace if (!@hasDecl(App, "SYSGPUInterface")) extern struct {
+    pub const SYSGPUInterface = core.sysgpu.Impl;
+} else struct {};
+
+pub fn main() !void {
+    // Run from the directory where the executable is located so relative assets can be found.
+    var buffer: [1024]u8 = undefined;
+    const path = std.fs.selfExeDirPath(buffer[0..]) catch ".";
+    std.os.chdir(path) catch {};
+
+    var gpa = std.heap.GeneralPurposeAllocator(.{}){};
+    defer _ = gpa.deinit();
+    core.allocator = gpa.allocator();
+
+    // Initialize GPU implementation
+    if (comptime core.options.use_wgpu) try core.wgpu.Impl.init(core.allocator, .{});
+    if (comptime core.options.use_sysgpu) try core.sysgpu.Impl.init(core.allocator, .{});
+
+    var app: App = undefined;
+    try app.init();
+    defer app.deinit();
+    while (!try core.update(&app)) {}
+}