ENH: Enabling soname support on FreeBSD.

Modules/Platform/FreeBSD.cmake

@@ -5,5 +5,7 @@ IF(EXISTS /usr/include/dlfcn.h)
   SET(CMAKE_SHARED_LIBRARY_LINK_C_FLAGS "")         # +s, flag for exe link to use shared lib
   SET(CMAKE_SHARED_LIBRARY_RUNTIME_C_FLAG "-Wl,-rpath,")       # -rpath
   SET(CMAKE_SHARED_LIBRARY_RUNTIME_C_FLAG_SEP ":")   # : or empty
+  SET(CMAKE_SHARED_LIBRARY_SONAME_C_FLAG "-Wl,-soname,")
+  SET(CMAKE_SHARED_LIBRARY_SONAME_CXX_FLAG "-Wl,-soname,")
 ENDIF(EXISTS /usr/include/dlfcn.h)
 # include the gcc flags