nautilus: build/ops: use gcc-8

[tchaikov]

we are using DTS-7 on CentOS7 and gcc-7 from ubuntu-toolchain-r PPA on xenial already for building nautilus.

we switched to GCC-8 in master for addressing ICE issues. these issues may or may not impact nautilus. and it's found that some builders are using GCC-8. even though install-deps.sh only installs gcc-7 if the installed GCC is lower than 7 on xenial. also, it's found that if we compile nautilus tree using GCC-7. we have

In file included from /home/jenkins-build/build/workspace/ceph-pull-requests/src/include/encoding.h:30:0,
                 from /home/jenkins-build/build/workspace/ceph-pull-requests/src/include/uuid.h:8,
                 from /home/jenkins-build/build/workspace/ceph-pull-requests/src/include/types.h:21,
                 from /home/jenkins-build/build/workspace/ceph-pull-requests/src/common/ceph_json.h:4,
                 from /home/jenkins-build/build/workspace/ceph-pull-requests/src/rgw/rgw_auth_keystone.cc:13:
/home/jenkins-build/build/workspace/ceph-pull-requests/src/common/ceph_time.h:504:16: warning: variable templates only available with -std=c++14 or -std=gnu++14
 constexpr bool converts_to_timespec_v = converts_to_timespec<Clock>::value;
                ^~~~~~~~~~~~~~~~~~~~~~

so, to ensure that we use the same compiler for building nautilus. let's move to GCC-8. also as a side-effect, the produced binary should be better because of the newer (and better) library, compiler and toolchain.

[smithfarm]

@tchaikov Cool, thanks! I'm not going to hit the merge button, yet, though - waiting for v14.2.3 tag to be added to the git repo.

[smithfarm]

test this please

[smithfarm]

jenkins test docs

[badone]

@tchaikov in the description did you actually mean to say "let's move to GCC-8" rather than "let's move to GCC-7"?

[yuriw]

wip-yuri-testing-2019-11-12-2351-nautilusyuriw