it was a copy-pasta error introduced by 2508d339. the copyright
blob was copied from a C++ source code, but the CMake language
define the block comment is different from the C++ language.
let's use the line comment of CMake.
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
Closesscylladb/scylladb#16615