disable use of libdl

Index: CMakeLists.txt
--- CMakeLists.txt.orig
+++ CMakeLists.txt
@@ -40,7 +40,7 @@ if(NOT VOLK_HEADERS_ONLY OR VOLK_INSTALL)
   if(VOLK_STATIC_DEFINES)
     target_compile_definitions(volk PUBLIC ${VOLK_STATIC_DEFINES})
   endif()
-  if (NOT WIN32)
+  if (NOT WIN32 AND NOT (CMAKE_SYSTEM_NAME MATCHES "OpenBSD"))
     target_link_libraries(volk PUBLIC dl)
   endif()
 endif()
@@ -54,7 +54,7 @@ target_include_directories(volk_headers INTERFACE
   $<BUILD_INTERFACE:${CMAKE_CURRENT_LIST_DIR}>
   $<INSTALL_INTERFACE:include>
 )
-if (NOT WIN32)
+if (NOT WIN32 AND NOT (CMAKE_SYSTEM_NAME MATCHES "OpenBSD"))
   target_link_libraries(volk_headers INTERFACE dl)
 endif()
 
