For Eclipse CDT Kepler what worked for me to get rid of std::thread
unresolved symbol is:
Go to Preferences->C/C++->Build->Settings
Select the Discovery tab
Select CDT GCC Built-in Compiler Settings [Shared]
Add the -std=c++11 to the "Command to get the compiler specs:" field such as:
${COMMAND} -E -P -v -dD -std=c++11 ${INPUTS}
Adding -std=c++11
to project Properties/C/C++ Build->Settings->Tool Settings->GCC C++ Compiler->Miscellaneous->Other
Flags wasn't enough for Kepler, however it was enough for older versions such as Helios.