[llvm] [ocaml] Support linking against dylib

[mgorny]

Summary

Support linking OCaml modules against LLVM dylib when requested,
rather than against static libs that might not be installed at all.

[mgorny]

@whitequark, ping.

[whitequark]

LGTM. I did not get a notification for this before for some reason.

[mgorny]

No problem. Thanks!

llvm/cmake/modules/AddOCaml.cmake

foreach( ocaml_dep ${ARG_OCAMLDEP} )
     get_target_property(dep_ocaml_flags "ocaml_${ocaml_dep}" OCAML_FLAGS)
     list(APPEND ocaml_flags ${dep_ocaml_flags})
   endforeach()
 
   if( NOT BUILD_SHARED_LIBS )
     list(APPEND ocaml_flags "-custom")
   endif()
 
+  if(LLVM_LINK_LLVM_DYLIB)
+    list(APPEND ocaml_flags "-lLLVM")
+  else()
     explicit_map_components_to_libraries(llvm_libs ${ARG_LLVM})
     foreach( llvm_lib ${llvm_libs} )
       list(APPEND ocaml_flags "-l${llvm_lib}" )
     endforeach()
 
     get_property(system_libs TARGET LLVMSupport PROPERTY LLVM_SYSTEM_LIBS)
     foreach(system_lib ${system_libs})
       if (system_lib MATCHES "^-")
         # If it's an option, pass it without changes.
         list(APPEND ocaml_flags "${system_lib}" )
       else()
         # Otherwise assume it's a library name we need to link with.
         list(APPEND ocaml_flags "-l${system_lib}" )
       endif()
     endforeach()
+  endif()
 
   string(REPLACE ";" " " ARG_CFLAGS "${ARG_CFLAGS}")
   set(c_flags "${ARG_CFLAGS} ${LLVM_DEFINITIONS}")
   foreach( include_dir ${LLVM_INCLUDE_DIR} ${LLVM_MAIN_INCLUDE_DIR} )
     set(c_flags "${c_flags} -I${include_dir}")
   endforeach()
   # include -D/-UNDEBUG to match dump function visibility
   # regex from HandleLLVMOptions.cmake