To work with the Perforce 2018.1 version it needs the older 1.0.1s OpenSSL libraries attached to the Perforce libraries to successfully compile.
Another possibility would be probably to compile Perforce to work with the newer 1.1.1 OpenSSl version that is default in Unreal 4.26.
First I placed the downloaded directory under “Engine/Source/ThirdParty/Perforce” and then I made some changes in Perforce.Build.cs to point to the added directory when building for linux.
Unfortunately I’m having a bunch of errors when trying to compile because a file called “libp4sslstub” is missing in the new folder and those errors remains even if I don´t add this file in Perfoce.Build.cs.
What did you do to include the file “libp4sslstub”?
Where is the file PerforceVersionControl.Build.cs?
Can you upload any screenshots showing your configuration?