nir,vtn: Add exported bool to nir_function

For optimizing libraries.

Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Reviewed-by: Konstantin Seurer <konstantin.seurer@gmail.com>
Reviewed-by: Karol Herbst <kherbst@redhat.com>
Reviewed-by: Faith Ekstrand <faith.ekstrand@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/25498>

src/compiler/nir/nir.h

@@ -3465,6 +3465,8 @@ typedef struct nir_function {
    nir_function_impl *impl;
 
    bool is_entrypoint;
+   /* from SPIR-V linkage, only for libraries */
+   bool is_exported;
    bool is_preamble;
    /* from SPIR-V function control */
    bool should_inline;