gallivm: use uint build context for mask instead of float

Unsurprisingly noone was using it except for grabbing builder.

Reviewed-by: Jose Fonseca <jfonseca@vmware.com>

src/gallium/auxiliary/gallivm/lp_bld_tgsi_soa.c

@@ -2851,7 +2851,7 @@ lp_build_tgsi_soa(struct gallivm_state *gallivm,
                                 max_output_vertices);
    }
 
-   lp_exec_mask_init(&bld.exec_mask, &bld.bld_base.base);
+   lp_exec_mask_init(&bld.exec_mask, &bld.bld_base.int_bld);
 
    bld.system_values = *system_values;