MFH: r497662

Add compiler:c++11-lang to USES to fix the following on GCC-based
architectures:

/usr/local/lib/libboost_filesystem.so: undefined reference to 'std::runtime_error::runtime_error(char const*)@GLIBCXX_3.4.21'

While here, pet portlint.

Approved by: portmgr (tier-2 blanket)