This data structure is used by the Zig language code generation and therefore must be kept in sync with the compiler implementation.
pub const VaListX86_64 = extern struct
pub const VaListX86_64 = extern struct {
gp_offset: c_uint,
fp_offset: c_uint,
overflow_arg_area: *anyopaque,
reg_save_area: *anyopaque,
}