Add euclidean_gcd in c++

[emn2]

For short term contributors: we understand that getting your commits well defined like we require is a hard task and takes some learning. If you look to help without wanting to contribute long term there's no need for you to learn this. Just drop us a message and we'll take care of brushing up your stuff for merge!

Fixes #{ISSUE_NUMBER}

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[TravisBuddy]

Hey @emn2, Something went wrong with the build.

TravisCI finished with status errored, which means the build failed because of something unrelated to the tests, such as a problem with a dependency or the build process itself.

View build log

TravisBuddy Request Identifier: 5030d340-04de-11eb-a4bc-1b94c014fd22

[emn2]

Hi @TravisBuddy,

Do you have any suggestions or hints on how to solve this problem?

[sangamcse]

@emn2, if you are really interested in contributing to this project then please go through community guidelines at least once(I see you have checked that box as well here but haven't followed that).