Since all supported versions of FreeBSD now have libc++ and libcxxrt in
the base system, and these ports were outdated, remove them, and update
any ports that still depended on them:
* graphics/gnash
* textproc/hs-double-conversion
* x11-toolkits/hs-wxc
* math/parmetis

Approved by:	portmgr (antoine)
Exp-run by:	antoine
PR:		217257
MFH:		2017Q1