checkMagic

pub fn checkMagic(bc: *BitcodeReader, magic: *const [4]u8) !void {
    var buffer: [4]u8 = undefined;
    try bc.readBytes(&buffer);
    if (!std.mem.eql(u8, &buffer, magic)) return error.InvalidMagic;

    try bc.startBlock(null, 2);
    try bc.block_info.put(bc.allocator, Block.block_info, Block.Info.default);
}