aco: Fixes compiling error about char8_t with c++20

cc @hakzsam fo review

cc @ms178 for test

The error is: ../mesa/src/amd/compiler/aco_register_allocation.cpp:382:7: error: no matching function for call to 'printf' printf(u8"☐");

Fixes: 209a89e5 ("aco: Convert to use u8 literal for Unicode character to fixes msvc warning")

Closes: #7318 (closed)

Signed-off-by: Yonggang Luo luoyonggang@gmail.com