BetCOM does not seem to build with clang

gcc seems to work though. The error that clang throws:

[  1%] Building CXX object src/BetCOM/CMakeFiles/BetCOM.dir/Actuator.pb.cc.o
In file included from /home/mernestus/topcore_orocos_packages/TopCoreIO/build/src/BetCOM/Actuator.pb.cc:5:
/home/mernestus/topcore_orocos_packages/TopCoreIO/build/src/BetCOM/Actuator.pb.h:7:10: fatal error: 'string' file not found
#include <string>
         ^
1 error generated.