ncurses: correct check for gcc >= 5.0

The hack in question is intended to workaround seemingly bogus #line markers
in cpp output. As far as I can tell, llvm cpp doesn't do this by default, so
there's no reason to add -P.

In our /bin/sh, the main incantation should be placed in a sub-shell in
order to properly pipe the output to fgrep.

The main motivation for this change is admittedly to stop emitting the noise
about clang not being gcc in make -s buildworld

MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D22952

Make ncurses build with GCC 5.0 and up

Merge the end result of two upstream changes:

Original fix from 20141206:
+ modify MKlib_gen.sh to work around change in development version of
gcc introduced here:
https://gcc.gnu.org/ml/gcc-patches/2014-06/msg02185.html
https://gcc.gnu.org/ml/gcc-patches/2014-07/msg00236.html
(reports by Marcus Shawcroft, Maohui Lei).

Later fixed in different manner in 20150725:
+ use alternate workaround for gcc 5.x feature (adapted from patch by
Mikhail Peselnik).

A new jail(8) with a configuration file, to replace the work currently done
by /etc/rc.d/jail.

Create the altix project branch. The altix project will add support
for the SGI Altix 350 to FreeBSD/ia64. The hardware used for porting
is a two-module system, consisting of a base compute module and a
CPU expansion module. SGI's NUMAFlex architecture can be an excellent
platform to test CPU affinity and NUMA-aware features in FreeBSD.

- Import the HEAD csup code which is the basis for the cvsmode work.

Import ncurses 5.6-20080209 snapshot onto the vender branch

Import ncurses 5.6-20071222 snapshot onto the vender branch

Import ncurses 5.6-20061217 onto the vender branch

Approved by: delphij

Import ncurses-5.2-20020518 onto the vendor branch.

Obtained from: ftp://dickey.his.com/ncurses/

Import ncurses-5.2-20010512 onto the vendor branch

Obtained from: ftp://dickey.his.com/ncurses/

Import ncurses-5.1-20001009 onto the vendor branch

Import unmodified (but trimmed) ncurses 5.0 prerelease 990821.
This contains the full eti (panel, form, menu) extensions.
bmake glue to follow.

Obtained from: ftp://ftp.clark.net/pub/dickey/ncurses