Fix FindIconv cmake module to correctly compile the c++ test code

cmake/Modules/FindIconv.cmake

@@ -35,6 +35,11 @@ find_package_handle_standard_args(Iconv REQUIRED_VARS ICONV_LIBRARIES ICONV_INCL
 #              char** outbuf, size_t* outbytesleft);
 if(ICONV_FOUND)
   include(CheckCXXSourceCompiles)
+
+  # Set the parameters needed to compile the following code.
+  set(CMAKE_REQUIRED_INCLUDES ${ICONV_INCLUDE_DIRS})
+  set(CMAKE_REQUIRED_LIBRARIES ${ICONV_LIBRARIES})
+
  check_cxx_source_compiles("
    #include <iconv.h>
    int main(){