make_unique doesn't compile with apple clang 13

[stevengj]

I'm getting

  CXX      GDSIIgeom.lo
GDSIIgeom.cpp:147:26: error: no member named 'make_unique' in namespace 'std'
    auto vertices = std::make_unique<vector3[]>(num_vertices);

on master with macOS 11.5.2 and Apple clang version 13.0.0 (clang-1300.0.29.3).

[stevengj]

Seems to be due to #1839, cc @kkg4theweb.

The issue is that this is a C++14 feature, I guess.

[stevengj]

Seems like it should be fine to replace this with an explicit unique_ptr, which is slightly more verbose but is otherwise equivalent.