security/botan110: make ECC mandatory

Boost >= 1.65 no longer provides TR1. However, GCC defaults to C++14
while libc++ leaks enough C++11 features that TR1 can be emulated in
C++98 mode.

PR: 220760
Approved by: portmgr blanket
Tested by: Dmitri Goutnik, Ralf van der Enden