Eigen + Boost.Python + gcc-7 = crash

I am using Boost.Python to provide bindings for a scientific app which uses [Eigen](http://eigen.tuxfamily.org/) for linear algebra. I am experiencing a segfault with some Eigen types, and I managed to isolate the code that causes the crash.

Please consider the [attached script](https://github.com/boostorg/python/files/2375991/test.txt) which:
* prepares a cpp file with a simple test case;
* builds the code with gcc-5, gcc-7, and gcc-8;
* runs the code from python.

As you can see from the comments at the bottom of the script, the test builds, but leads to a crash when run. This does not happen with gcc-5.

Interestingly, I can reproduce the problem by using `Matrix2d` and `Vector2d`; but it does **not** happen when using `Matrix3d` or `Vector3d` (this can be easily verified by replacing in the attached script).

Now, while the problem can be in any of the 3 components (Eigen, Boost.Python, gcc-7), I decided to post an issue here first because the project we are building uses Eigen extensively, and I never experienced any problem on "C++ side", even while building with gcc-7.

I hope that someone with experience with the Boost.Python internals can help me shed some light on this.

Some more info about the build system, in case it might be useful:
* `Ubuntu 16.04` running kernel `4.4.0-134-generic`
* `gcc version 5.5.0 20171010 (Ubuntu 5.5.0-12ubuntu1~16.04)` from apt package `build-essentials`
* `gcc version 7.3.0 (Ubuntu 7.3.0-21ubuntu1~16.04) ` from [PPA](https://launchpad.net/~ubuntu-toolchain-r/+archive/ubuntu/test)
* `gcc version 8.1.0 (Ubuntu 8.1.0-5ubuntu1~16.04)` from [PPA](https://launchpad.net/~ubuntu-toolchain-r/+archive/ubuntu/test)
* `boost 1.66` from [here](https://dl.bintray.com/boostorg/release/1.66.0/source/boost_1_66_0.tar.bz2) built with b2 (just as test, I tried building it with both gcc-5 and gcc-7, with no difference);
* `boost 1.58` from apt package `libboost-all-dev`.