Enable IN_LIST in older CMake

[ferdnyc]

Should fix #510 breakage on gitlab builders.

[codecov]

Codecov Report

Merging #542 into develop will decrease coverage by 0.03%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           develop     #542      +/-   ##
===========================================
- Coverage    48.81%   48.77%   -0.04%     
===========================================
  Files          129      129              
  Lines        10042    10035       -7     
===========================================
- Hits          4902     4895       -7     
  Misses        5140     5140              

Impacted Files	Coverage Δ
src/FFmpegWriter.cpp	62.48% <0.00%> (-0.28%)	⬇️
include/DummyReader.h	0.00% <0.00%> (ø)

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[jonoomph]

Linux builder is happy now! Nice!

[ferdnyc]

Yeah, I guess technically this increases our minimum CMake version to 3.3 (which is where IN_LIST was introduced) — I could've also fixed this by changing the version range to 3.3...3.17 here:

libopenshot/CMakeLists.txt

Line 27 in 85b6a96

cmake_minimum_required(VERSION 3.2...3.14 FATAL_ERROR)

Which would've made CMP0057 default to NEW behavior automatically. I guess in CMake 3.7 (version on the Linux builder) it was still defaulting to OLD, though they obviously dropped that at some point after.

Trying to build libopenshot with CMake 3.2 will likely now break when it hits the IN_LIST, but really who's going to try to do that? ¯\_(ツ)_/¯

[jonoomph]

...but really who's going to try to do that? ¯\_(ツ)_/¯

I guess we'll find out! haha