Check for libdl, and only use it when available

[dim]

Summary

On BSDs, there is no libdl.so, and functions like dlopen are implemented in the main C library instead. Check for the existence of libdl in the main CMakeLists.txt file, and only use it if it exists.

[jlpeyton]

CMake has a variable CMAKE_DL_LIBS which I believe contains the information you want. It essentially gets defined to "-ldl" on unices that need it and "" on platforms which don't need it.

[dim]

In D34632#790913, @jlpeyton wrote:

CMake has a variable CMAKE_DL_LIBS which I believe contains the information you want. It essentially gets defined to "-ldl" on unices that need it and "" on platforms which don't need it.

Hm, this isn't used in the main LLVM build though. I basically copied what is done in cmake/config-ix.cmake there. But I'll have a look at CMAKE_DL_LIBS, I wonder which version of CMake introduced that variable, the documentation doesn't specify it.

[dim]

Use CMAKE_DL_LIBS instead. This is in CMake since at least 2012, if not before.

openmp/trunk/libomptarget/CMakeLists.txt

set(src_files
     src/omptarget.cpp
   )
   
   include_directories(src/)
   
   # Build libomptarget library with libdl dependency.
   add_library(omptarget SHARED ${src_files})
   target_link_libraries(omptarget
-    dl
+    ${CMAKE_DL_LIBS}
     "-Wl,--version-script=${CMAKE_CURRENT_SOURCE_DIR}/exports")
   
   # Install libomptarget under the lib destination folder.
   install(TARGETS omptarget LIBRARY DESTINATION lib${LIBOMPTARGET_LIBDIR_SUFFIX})
   
   # Retrieve the path to the resulting library so that it can be used for 
   # testing.
   get_target_property(LIBOMPTARGET_LIBRARY_DIR omptarget LIBRARY_OUTPUT_DIRECTORY)