GH-102711: Fix warnings found by clang (#102712)

There are some warnings if build python via clang:

Parser/pegen.c:812:31: warning: a function declaration without a prototype is deprecated in all versions of C [-Wstrict-prototypes]
_PyPegen_clear_memo_statistics()
                              ^
                               void

Parser/pegen.c:820:29: warning: a function declaration without a prototype is deprecated in all versions of C [-Wstrict-prototypes]
_PyPegen_get_memo_statistics()
                            ^
                             void

Fix it to make clang happy.

Signed-off-by: Chenxi Mao <chenxi.mao@suse.com>