Upgrade gentoo

Upgrading to PHP 7

edit /etc/portage/make.conf

# APACHE2_MODULES: update -D PHP5 to -D PHP
# add php7-0 as target
PHP_TARGETS="php5-6 php7-0"

emerge everything
use eselect to select it

Upgrading to gentoo profile v17

bitpost ~ # eselect profile list
Available profile symlink targets:
 [1]   default/linux/amd64/13.0 (stable)
 ...
 [9]   default/linux/amd64/13.0/no-multilib (stable)
 ...
 [12]  default/linux/amd64/17.0 (stable) *
 ...
 [22]  default/linux/amd64/17.0/no-multilib (stable) *
 ...
 [27]  default/linux/amd64/17.1 (exp)
 ...

I started down v17 so I better finish up. But let's go with the base profile (12). I used to use no-multilib (to avoid 32-bit support) but it sounds like there's little harm or cost in it.

Steps are described in eselect:

 eselect news list
 eselect news read 36
 2017-11-30-new-17-profiles
  Title                     New 17.0 profiles in the Gentoo repository
(blah blah blah)
* Rebuild your entire system
    emerge -e @world
Switching the profile from 13.0 to 17.0 modifies the settings of 
GCC 6 to generate PIE executables by default; thus, you need to do 
the rebuilds even if you have already used GCC 6 beforehand.
If you do not follow these steps you may get spurious build
failures when the linker tries unsuccessfully to combine non-PIE
and PIE code.