JIT: Fix compiler warning from visibility attribute in typedef

[savannahostrowski]

/Users/runner/work/cpython/cpython/Tools/jit/trampoline.c:13:13: warning: 'visibility' attribute ignored [-Wignored-attributes]
   13 |     typedef DECLARE_TARGET((*jit_func));
      |             ^
/Users/runner/work/cpython/cpython/Tools/jit/jit.h:11:49: note: expanded from macro 'DECLARE_TARGET'
   11 |     _Py_CODEUNIT *__attribute__((preserve_none, visibility("hidden"))) \
      |

This was introduced in #136528. The DECLARE_TARGET macro includes visibility("hidden"), which is valid for forward declarations but gets ignored when used in a typedef, so the compiler is yelling.