fix clang-10 support

[bjornstromberg]

• added preprocessor directives to:
  • support for clang/llvm >= 10 which uses smartptr's instead of rawpointers.
  • support for clang/llvm < 10 which uses raw pointers.
  • bump required C++ version from 11 to 14,
    since Clang-10 requires C++14 to build, and clang-9 builds fine with it.

tested so it builds fine with clang-9 + clang-10.

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[bjornstromberg]

well i wont sign any CLA, i'm no lawyer and i don't care that much to read into the agreement.
I've made the changes public on github, should be sufficent for GPLv3.

so i guess that will make this upstream pull request will never get merged.