s2s in falcON fails for gcc-11

[teuben]

As seen on ubuntu 21.10:

    s2s p1024.in p1024.out3 filter='i<#0' params=512

fails with

falcON Error: bodyfunc::bodyfunc(): could not compile expression; perhaps it contains a syntax error

[teuben]

deja vu on this.... was this due to otf compilation wasn't the same as the one via the makedefs/Makefile ?

[teuben]

voila, the default is now -std=c++17, and it seems falcON needs -std=c++14 or below. I've decided on c++11, since code was developed as late as 2011. See code fix in falcON/src/public/lib/bodyfunc.cc where this is now hardcoded to be c++11.

[teuben]

See also #56