[Fixup] Add FAQ entry for GCC missing errors

[kadler]

What improvement(s) could be made?

Users trying to build C/C++ applications tend to run in to issues with missing GCC and don't know how to solve. We should add FAQ entries for common gcc and g++ missing errors (and possibly gcc-cpp, since I don't think gcc6 package requires it).

unable to execute 'gcc': No such file or directory

Solution: yum install gcc or yum group install "Development Tools"

gcc-6.bin: error trying to exec 'cc1plus': execvp: No such file or directory

Solution: yum install gcc-cplusplus or yum group install "Development Tools"

collect2: fatal error: library libstdc++ not found

Solution: yum install libstdcplusplus-devel