gpu-dawn: clone mach-glfw if needed (temporary)

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

gpu-dawn/build.zig

@@ -7,6 +7,12 @@ pub fn build(b: *Builder) void {
     const mode = b.standardReleaseOptions();
     const target = b.standardTargetOptions(.{});
 
+    // TODO(build-system): remove dependency on GLFW (Dawn no longer requires it / we can
+    // eliminate it.)
+    if (!dirExists("libs/mach-glfw")) {
+        try gitClone(b.allocator, "https://github.com/hexops/mach-glfw", "libs/mach-glfw");
+    }
+
     const lib = b.addStaticLibrary("gpu", "src/main.zig");
     lib.setBuildMode(mode);
     lib.setTarget(target);
@@ -306,6 +312,15 @@ fn getCurrentGitCommit(allocator: std.mem.Allocator) ![]const u8 {
     return result.stdout;
 }
 
+fn gitClone(allocator: std.mem.Allocator, repository: []const u8, dir: []const u8) !bool {
+    const result = try std.ChildProcess.exec(.{
+        .allocator = allocator,
+        .argv = &.{ "git", "clone", repository, dir },
+        .cwd = thisDir(),
+    });
+    return result.term.Exited == 0;
+}
+
 fn downloadFile(allocator: std.mem.Allocator, target_file: []const u8, url: []const u8) !void {
     std.debug.print("downloading {s}..\n", .{url});
     const child = try std.ChildProcess.init(&.{ "curl", "-L", "-o", target_file, url }, allocator);