gpu: add gpu-hello-triangle (dawn) example

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

gpu/build.zig

@@ -1,17 +1,28 @@
 const std = @import("std");
+const gpu_dawn = @import("libs/mach-gpu-dawn/build.zig");
+const glfw = @import("libs/mach-glfw/build.zig");
 
 pub fn build(b: *std.build.Builder) void {
-    // Standard release options allow the person running `zig build` to select
-    // between Debug, ReleaseSafe, ReleaseFast, and ReleaseSmall.
     const mode = b.standardReleaseOptions();
+    const target = b.standardTargetOptions(.{});
 
     const lib = b.addStaticLibrary("gpu", "src/main.zig");
     lib.setBuildMode(mode);
     lib.install();
+    gpu_dawn.link(b, lib, .{});
 
     const main_tests = b.addTest("src/main.zig");
     main_tests.setBuildMode(mode);
 
     const test_step = b.step("test", "Run library tests");
     test_step.dependOn(&main_tests.step);
+
+    const example = b.addExecutable("gpu-hello-triangle", "examples/main.zig");
+    example.setTarget(target);
+    example.setBuildMode(mode);
+    example.install();
+    example.linkLibC();
+    example.addPackagePath("glfw", "libs/mach-glfw/src/main.zig");
+    glfw.link(b, example, .{});
+    gpu_dawn.link(b, example, .{});
 }