MFH: r446855

Explicitly build with -std=gnu++11.

This fixes the build with GCC 6, which switched its default from -std=gnu++98
to -std=gnu++14. With this switch, it added a `operator delete(void*, size_t)'
overload and uses it for all delete calls. This does not play well with
dependencies built with other compilers (such as base clang), which use the old
operator delete overload and cause linking errors.

PR: 219484
Submitted by: fernando.apesteguia@gmail.com (maintainer)

Approved by: ports-secteam (with hat)