sokol_gfx.h: fix _sg_u128 linkage visibility
@@ -16598,7 +16598,7 @@ typedef struct {
uint64_t lo, hi;
} _sg_u128_t;
-_sg_u128_t _sg_u128(void) {
+_SOKOL_PRIVATE _sg_u128_t _sg_u128(void) {
_sg_u128_t res;
_sg_clear(&res, sizeof(res));
return res;