build: cmake: add check-header target

to have feature parity with `configure.py`. we won't need this
once we migrate to C++20 modules. but before that day comes, we
need to stick with C++ headers.

we generate a rule for each .hh files to create a corresponding
.cc and then compile it, in order to verify the self-containness of
that header. so the number of rule is quite large, to avoid the
unnecessary overhead. the check-header target is enabled only if
`Scylla_CHECK_HEADERS` option is enabled.

Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>

Closes scylladb/scylladb#15913

locator/CMakeLists.txt

@@ -32,3 +32,6 @@ target_link_libraries(scylla_locator
     db)
 
 add_whole_archive(locator scylla_locator)
+
+check_headers(check-headers scylla_locator
+  GLOB_RECURSE ${CMAKE_CURRENT_SOURCE_DIR}/*.hh)