[OCaml] Install .mli (interface) files

[mgorny]

Summary

Install the OCaml interface .mli files. Those files were most likely omitted because they are input files for the compiled .cmi files. However, installing them is reasonable since -- unlike .cmi files -- they are human-readable.

The issue was originally spotted by @jpdeplaix.

[whitequark]

LGTM

[mgorny]

Thanks. Committing now.

cmake/modules/AddOCaml.cmake

foreach( llvm_lib ${llvm_libs} )
       add_dependencies("ocaml_${name}" "${llvm_lib}")
     endforeach()
   endif()
 
   add_dependencies("ocaml_all" "ocaml_${name}")
 
   set(install_files)
   set(install_shlibs)
-  foreach( ocaml_output ${ocaml_outputs} )
+  foreach( ocaml_output ${ocaml_inputs} ${ocaml_outputs} )
     get_filename_component(ext "${ocaml_output}" EXT)
 
     if( NOT (ext STREQUAL ".cmo" OR
+             ext STREQUAL ".ml" OR
              ext STREQUAL CMAKE_C_OUTPUT_EXTENSION OR
              ext STREQUAL CMAKE_SHARED_LIBRARY_SUFFIX) )
       list(APPEND install_files "${ocaml_output}")
     elseif( ext STREQUAL CMAKE_SHARED_LIBRARY_SUFFIX)
       list(APPEND install_shlibs "${ocaml_output}")
     endif()
   endforeach()