symbiotic-build.sh: allow building with gcc 6 and higher
symbiotic-build.sh: allow building with gcc 6 and higher

I have gcc 6 and klee fails to build because it cannot find a suitable
compiler (by clang is broken).

So allow not only gcc 5, but also gcc 6-9 :).

Signed-off-by: Jiri Slaby <dfbf39eb5bf303a3db5454d815cb8c8888cbadf9@suse.cz>

staticafi/symbiotic,staticafi/symbiotic,staticafi/symbiotic,staticafi/symbiotic