You must have had a mixup of versions. TStringHashList used to be in lcl before version 1.8 and got the strings from lclstrconsts. Now it is in components/lazutils and uses the strings from lazutilsstrconsts as GetMem writes. So, if you run Lazarus 1.8RC but find TStringHashList in lcl your installation somewhere must have had a path pointing to the wrong directory.
Yes, reinstallation of into a clean directory and a clean user profile folder is usually the quickest way to solve these issues.