- The -Wno-deprecated-copy flag for gcc-9.2.0

  In the future we may indeed wish to explicitly request default
  generated constructors and assignment operators, but at the moment
  these are still acceptable.

- The -Wno-alloc-size-larger-than flag for mingw compilations

  Related to differences in PTRDIFF_MAX vs SIZE_MAX on the target.
  Several issues related to this can be found in the gcc bug reports
  and on stackoverflow etc.