net/fort: don't depend on gcc10, fix version check

The current version of FORT builds fine with any c11 compiler.  There is
no need for USE_GCC.

Patch the build system to correctly define the version of FORT as seen
in the output of "fort --version" and the "User-Agent:" HTTP header. [1]

Approved by:	Toni Yannick Kalombo <toni@devboks.com> (maintainer)
Reported by:	Mark Tinka <mark@tinka.africa> [1]