gpu-dawn: fix duplicate symbol main on x86_64-linux

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

gpu-dawn/build.zig

@@ -13,7 +13,7 @@ pub fn build(b: *Builder) void {
 
     // Just to demonstrate/test linking. This is not a functional example, see the mach/gpu examples
     // or Dawn C++ examples for functional example code.
-    const example = b.addExecutable("dawn-example", "src/dawn/dummy.zig");
+    const example = b.addExecutable("dawn-example", "src/main.zig");
     example.setBuildMode(mode);
     example.setTarget(target);
     link(b, example, options);

gpu-dawn/src/dawn/dummy.zig

@@ -1 +0,0 @@
-pub fn main() void {}

gpu-dawn/src/main.zig

@@ -0,0 +1 @@
+pub fn main() void {}