Add c++11 to USE_LANGUAGES

[Sevan Janiyan <venture37%geeklan.co.uk@localhost>]

Hello,
We're starting to see applications which specifically need a compiler
with C++ 11 support in order to build correctly e.g. textproc/icu &
net/powerdns-recursor.

The patch below adds a minimal set of changes similar to the c99 option
which results in GCC_REQD being set to 4.8 & -std=c++11 being handled by
the wrapppers.

http://www.netbsd.org/~sevan/patch-pkgsrc-cplusplus11.txt

Any comments?



Sevan