on linux you must define RMLCLTRUNK for richmemopackage.lpk and richmemo_design.lpk (Options > Compiler Options > Custom Options > Define ...)
on windows compile for me.
Windows 10 x64, Lazarus trunk r65116 and FPC 3.2.0 32-bit
Debian 10 x64, Lazarus trunk r65116 and FPC 3.2.0 x64