GLSL samples: add empty entry point if needed.

If a WGSL test contains no entry points, add an empty one.
In that case, do not pass its name to the generator, so we
generate code for all functions, so they aren't culled for
reachability.

Add new test results for formerly empty tests.

Bug: tint:1376
Change-Id: Ibf371b943fb273d44712dfcc9dc1b7bb4ab071db
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/76540
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>
Commit-Queue: Stephen White <senorblanco@chromium.org>

test/expressions/zero_init/vec4/bool.wgsl.expected.glsl

@@ -0,0 +1,16 @@
+#version 310 es
+precision mediump float;
+
+layout(local_size_x = 1, local_size_y = 1, local_size_z = 1) in;
+void unused_entry_point() {
+  return;
+}
+void main() {
+  unused_entry_point();
+}
+
+
+
+void f() {
+  bvec4 v = bvec4(false, false, false, false);
+}

test/expressions/zero_init/vec4/f32.wgsl.expected.glsl

@@ -0,0 +1,16 @@
+#version 310 es
+precision mediump float;
+
+layout(local_size_x = 1, local_size_y = 1, local_size_z = 1) in;
+void unused_entry_point() {
+  return;
+}
+void main() {
+  unused_entry_point();
+}
+
+
+
+void f() {
+  vec4 v = vec4(0.0f, 0.0f, 0.0f, 0.0f);
+}

test/expressions/zero_init/vec4/i32.wgsl.expected.glsl

@@ -0,0 +1,16 @@
+#version 310 es
+precision mediump float;
+
+layout(local_size_x = 1, local_size_y = 1, local_size_z = 1) in;
+void unused_entry_point() {
+  return;
+}
+void main() {
+  unused_entry_point();
+}
+
+
+
+void f() {
+  ivec4 v = ivec4(0, 0, 0, 0);
+}

test/expressions/zero_init/vec4/u32.wgsl.expected.glsl

@@ -0,0 +1,16 @@
+#version 310 es
+precision mediump float;
+
+layout(local_size_x = 1, local_size_y = 1, local_size_z = 1) in;
+void unused_entry_point() {
+  return;
+}
+void main() {
+  unused_entry_point();
+}
+
+
+
+void f() {
+  uvec4 v = uvec4(0u, 0u, 0u, 0u);
+}