Load Engine Source into Perforce - Unable to add Engine\Source\Runtime\SymsLib/lib/x64/Release/SymsLib.lib

You can run the ...\Engine\Source\Runtime\SymsLib\SymsLib.sln and set it to Release , x64 and build it (F7).
It will create SymsLib.lib in ...\SymsLib\lib\x64\Release.

Also, worth looking at this recommendation for p4ignore.