$ emerge -pv glibc binutils binutils-libs

These are the packages that would be merged, in order:

Calculating dependencies  ...... done!
[ebuild     U ~] net-dns/libidn2-2.0.5::gentoo [2.0.4::gentoo] USE="-static-libs" ABI_X86="(64) -32 (-x32)" 2,043 KiB
[ebuild     U *] sys-libs/glibc-9999:2.2::gentoo [2.25-r11:2.2::gentoo] USE="multiarch%* (multilib) -audit -caps (-cet) (-compile-locales) -doc% -gd (-hardened) -headers-only -nscd -profile (-selinux) -suid -systemtap -test% (-vanilla) (-debug%) (-rpc%*)" 2,352 KiB
[ebuild  NS    ] sys-devel/binutils-2.30-r4:2.30::gentoo [2.29.1-r1:2.29.1::gentoo] USE="cxx nls -doc -multitarget -static-libs -test" 20,389 KiB
[ebuild  r  U ~] sys-libs/binutils-libs-2.31.1-r1:0/2.31.1-r1::gentoo [2.29.1-r1:0/2.29.1::gentoo] USE="nls -64-bit-bfd -multitarget -static-libs" ABI_X86="(64) -32 (-x32)" 20,001 KiB
[ebuild   R   ~] dev-python/setuptools-38.5.1::gentoo  USE="-test" PYTHON_TARGETS="python2_7 python3_4* python3_5 python3_6* -pypy -pypy3" 0 KiB
[ebuild     U  ] dev-python/certifi-2018.4.16::gentoo [2017.4.17::gentoo] PYTHON_TARGETS="python2_7 python3_4* python3_5 python3_6* (-pypy) (-pypy3) (-python3_7)" 147 KiB
[ebuild     U  ] dev-util/meson-0.46.1::gentoo [0.44.1::gentoo] PYTHON_TARGETS="python3_5 python3_6* (-python3_4%)" 1,176 KiB
[ebuild  N     ] x11-base/xorg-proto-2018.4::gentoo  483 KiB
[ebuild  rR    ] x11-libs/cairo-1.14.12::gentoo  USE="X glib opengl svg xcb (-aqua) -debug (-gles2) -static-libs -valgrind" ABI_X86="(64) -32 (-x32)" 0 KiB

Total: 9 packages (5 upgrades, 1 new, 1 in new slot, 2 reinstalls), Size of downloads: 46,588 KiB

!!! Multiple package instances within a single package slot have been pulled
!!! into the dependency graph, resulting in a slot conflict:

sys-libs/binutils-libs:0

  (sys-libs/binutils-libs-2.31.1-r1:0/2.31.1-r1::gentoo, ebuild scheduled for merge) pulled in by
    sys-libs/binutils-libs (Argument)

  (sys-libs/binutils-libs-2.29.1-r1:0/2.29.1::gentoo, installed) pulled in by
    sys-libs/binutils-libs:0/2.29.1= required by (dev-db/mariadb-10.1.31-r1:0/18::gentoo, installed)
                          ^^^^^^^^^^                                                                 

sys-libs/glibc:2.2

  (sys-libs/glibc-9999:2.2/2.2::gentoo, ebuild scheduled for merge) pulled in by
    sys-libs/glibc (Argument)

  (sys-libs/glibc-2.25-r11:2.2/2.2::gentoo, installed) pulled in by
    <sys-libs/glibc-2.26 required by (net-libs/libnsl-0:0/1::gentoo, installed)
    ^               ^^^^                                                        


!!! The slot conflict(s) shown above involve package(s) which may need to
!!! be rebuilt in order to solve the conflict(s). However, the following
!!! package(s) cannot be rebuilt for the reason(s) shown:

  (dev-db/mariadb-10.1.31-r1:0/18::gentoo, installed): ebuild is masked or unavailable


It may be possible to solve this problem by using package.mask to
prevent one of those packages from being selected. However, it is also
possible that conflicting dependencies exist such that they are
impossible to satisfy simultaneously.  If such a conflict exists in
the dependencies of two different packages, then those packages can
not be installed simultaneously.

For more information, see MASKED PACKAGES section in the emerge man
page or refer to the Gentoo Handbook.


The following packages are causing rebuilds:

  (sys-libs/binutils-libs-2.31.1-r1:0/2.31.1-r1::gentoo, ebuild scheduled for merge) causes rebuilds for:
    (x11-libs/cairo-1.14.12:0/0::gentoo, ebuild scheduled for merge)

The following keyword changes are necessary to proceed:
 (see "package.accept_keywords" in the portage(5) man page for more details)
# required by @__auto_slot_operator_replace_installed__ (argument)
=sys-libs/binutils-libs-2.31.1-r1 ~amd64

 * In order to avoid wasting time, backtracking has terminated early
 * due to the above autounmask change(s). The --autounmask-backtrack=y
 * option can be used to force further backtracking, but there is no
 * guarantee that it will produce a solution.

!!! The following installed packages are masked:
- sys-libs/glibc-2.25-r11::gentoo (masked by: package.mask)
/usr/portage/profiles/package.mask:
# Michał Górny <mgorny@gentoo.org>, Andreas K. Hüttel <dilfridge@gentoo.org>,
# Matthias Maier <tamiko@gentoo.org> (21 May 2017 and later updates)
# These old versions of toolchain packages (binutils, gcc, glibc) are no
# longer officially supported and are not suitable for general use. Using
# these packages can result in build failures (and possible breakage) for
# many packages, and may leave your system vulnerable to known security
# exploits.
# If you still use one of these old toolchain packages, please upgrade (and
# switch the compiler / the binutils) ASAP. If you need them for a specific
# (isolated) use case, feel free to unmask them on your system.

- sys-libs/binutils-libs-2.29.1-r1::gentoo (masked by: package.mask)
- dev-perl/DBD-mysql-4.41.0::gentoo (masked by: package.mask)
/usr/portage/profiles/package.mask:
# Kent Fredric <kentnl@gentoo.org> (27 May 2018)
# Subject to Man-in-the-middle security bypass vulnerability.
# Retained in tree only for users who need older versions
# for compatibility reasons.
# Bug: #623942

- net-libs/libnsl-0::gentoo (masked by: package.mask)
/usr/portage/profiles/package.mask:
# Andreas K. Hüttel <dilfridge@gentoo.org> (11 Sep 2018)
# Mask transition ebuilds that were needed only for <glibc-2.26
# We will keep them in the tree as long as we have masked
# <glibc-2.26.

- app-eselect/eselect-mesa-0.0.10-r1::gentoo (masked by: package.mask)
/usr/portage/profiles/package.mask:
# Matt Turner <mattst88@gentoo.org> (29 Sep 2018)
# Removal in 30 days, bug #576334

For more information, see the MASKED PACKAGES section in the emerge
man page or refer to the Gentoo Handbook.