requiring c++11 on icu?

[coypu%sdf.org@localhost]

there is already GCC_REQD+=4.8
it doesn't build when built for older C++ standards, e.g.:
https://nyftp.netbsd.org/pub/pkgsrc/packages/reports/2018Q2/NetBSD-6.0-x86_64/20180716.1407/icu-61.1/build.log

that can probably be patched, but since we already require a
compiler that accepts -std=gnu++11, why not avoid the patch?

(the rest are not seeing it because newer compiler versions default to
c++11)