std.builtin: add CallingConvention.x86_64_x32

This was forgotten during the refactoring of std.builtin.CallingConvention. It
mirrors mips64_n32 for MIPS.
beb507a1edAlex Rønne Petersen committed on 10/23/2025, 7:27:17 AMparenta144194
6 files changedLine totals unavailable