vulkan: Don't emit library_arch if the library_path is just a basename

If the library_path is just a basename like `libvulkan_lvp.so`, then
we can share the same JSON manifest between all of the architectures,
like we already do for Vulkan layers. This is also how the Nvidia
proprietary driver works, and how Mesa is packaged in Debian 13.
However, this will only work if we don't mark the manifest as being
architecture-specific.

This partially reverts commit f7aa6ba9 "vulkan: Specify library_arch in
ICD files".

Signed-off-by: Simon McVittie <smcv@collabora.com>
Reviewed-by: Mel Henning <mhenning@darkrefraction.com>
Reviewed-by: Matt Turner <mattst88@gmail.com>
Reviewed-by: Eric Engestrom <eric@igalia.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/37314>

src/vulkan/util/vk_icd_gen.py

@@ -75,7 +75,7 @@ if __name__ == '__main__':
         },
     }
 
-    if args.sizeof_pointer:
+    if args.sizeof_pointer and ('/' in lib_path or '\\' in lib_path):
         bit_width = args.sizeof_pointer * 8
         if bit_width in [32, 64]:
             json_data['ICD']['library_arch'] = str(bit_width)