Do I need to have imake/xmkmf?
No. LessTif used to work with those, but they became more of a problem than a solution, so we switched to GNU autoconf, which has the additional capability to find out many many things about the target platform while auto-configuring itself. Around December 1997 we also started to work with libtool and automake, two more free tools. They should solve the portability problems with building shared libraries on multiple platforms for us. You’ll find this in distributions of LessTif starting with release 0.85.