FindXMLRPC: Avoid hen egg issues during XMLRPC find
When building a project depending on xmlrpc-c on windows the utility xmlrpc-c-config is not available due to the fact it is a bash script in the upstream project. The variable XMLRPC_C_FOUND can not overwritten by the CMake command line nor the pre populated cache. So the only way to succeed this find script under windows is removing the XMLRPC_C_FOUND from the required variables.
Signed-off-by: Christian Ege christian.ege@ifm.com