compilers: install GCC 8 /CLANG 7 (as V8 does)

[refack]

Chromium and V8 are actually build with a very recent revision off the LLVM dev branch (svn revision 344066 which is ver 8 that is in progress)

GCC 8.1 has been available since May 2018 (http://gnu.mirrors.pair.com/gcc/gcc-8.1.0/) with 8.2 the latest.
CLang 7 has been available since Sep 2018 (http://releases.llvm.org/).
We are already using a very advanced MSVC compiler.

Using the latest compiler includes the latest optimizers, which is free performance gain. It also enables new C++ language fatures which can make the code simpler, and safer.

As I see it we need to make sure we can do this, then recommend an update to core.

/CC @nodejs/build @nodejs/release

[targos]

/cc @hashseed who told me that V8 is currently blocked by us because we still support GCC 4.9. They would like to start using C++14 features for which support was added in GCC 5

[nschonni]

Is this for 11? Otherwise what is the impact for native add-on building if introduced in 10

[refack]

Is this for 11? Otherwise what is the impact for native add-on building if introduced in 10

This will probably be for 12.

[hashseed]

Whether it's Node 11 or Node 12 is not particularly relevant for V8, since we take a snapshot of the master branch from time to time to use for our CI.

[mhdawson]

@gdams FYI, need to figure out plan for newer compiler on IBM platforms.

[rvagg]

I think we should probably start making moves in this direction for master for Node 12. #1583 is about release builds, I think devtoolset-7 might make sense on CentOS 7 for that. But we'll need to assess what we can do across our Linux test cluster, I'm sure there are going to be awkward edges.

For instance, Debian Stable (stretch) doesn't come with gcc-8, it's queued in Testing & Unstable. Thankfully Ubuntu 18.04 has it though.

[refack]

For instance, Debian Stable (stretch) doesn't come with gcc-8, it's queued in Testing & Unstable. Thankfully Ubuntu 18.04 has it though.

I'm more concerned with the IBM machines. It might be worth considering switching to clang for those, as it seems LLVM is easier to bootstrap.

[rvagg]

clang might be easier in lots of places, https://apt.llvm.org/ is pretty helpful. We'd need to balance that against needing to have gcc compilability tested though unless we're prepared to say gcc isn't a Tier 1 supported compiler.

[refack]

We can just barely still say that since it's not for V8...

[hashseed]

We still have a bot that tests building with GCC. We would love to get rid of it though :)