New port: devel/linux-c7-strace

strace is a system call tracer, i.e. a debugging tool which prints out a trace
of all the system calls made by a another process/program.

strace is similar to the native BSD ``truss'' utility, but it's output style is
more convenient in most cases.

For strace to work, linprocfs has to be mounted. FreeBSD does not mount it by
default. For more information, man linprocfs.

WWW: https://sourceforge.net/projects/strace/

Note that this does not currently work quite well; the kernel part
is coming soon.

Reviewed by: tijl
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D20030