Fix -Wstrict-prototypes in webgpu.h

Bug: https://github.com/webgpu-native/webgpu-headers/issues/151
Change-Id: Ifb884478b45b9c069696b61ce95e56dbe53a96e1
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/83820
Auto-Submit: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Austin Eng <enga@chromium.org>
Reviewed-by: Loko Kung <lokokung@google.com>
Commit-Queue: Loko Kung <lokokung@google.com>

generator/templates/api.h

@@ -116,9 +116,13 @@ extern "C" {
 
 {% for type in by_category["function pointer"] %}
     typedef {{as_cType(type.return_type.name)}} (*{{as_cType(type.name)}})(
+        {%- if type.arguments == [] -%}
+            void
+        {%- else -%}
             {%- for arg in type.arguments -%}
                 {% if not loop.first %}, {% endif %}{{as_annotated_cType(arg)}}
             {%- endfor -%}
+        {%- endif -%}
     );
 {% endfor %}