Fix find_soname when lld is the system linker

--- cmake/scripts/freebsd/Macros.cmake.orig	2017-12-21 00:17:03 UTC
+++ cmake/scripts/freebsd/Macros.cmake
@@ -73,8 +73,8 @@ function(find_soname lib)
   string(STRIP "${${lib}_FILENAME}" ${lib}_FILENAME)
   if(NOT ${lib}_FILENAME)
     execute_process(COMMAND ${CMAKE_C_COMPILER} -nostdlib -o /dev/null -Wl,-t ${link_lib}
-                    OUTPUT_QUIET
-                    ERROR_VARIABLE _TMP_FILENAME)
+                    ERROR_QUIET
+                    OUTPUT_VARIABLE _TMP_FILENAME)
     string(REGEX MATCH ".*lib${liblow}.so" ${lib}_FILENAME ${_TMP_FILENAME})
   endif()
   if(${lib}_FILENAME)
