I haven't dug into the source code for this, but I too have noticed that (1) I can move around a Windows compilation of tcc that was built using the build-tcc.bat file, but (2) I cannot move around a compilation built using ./configure. This has ramifications for the build recipe for Alien::TinyCC, which is why I know and care. :-)
If I were to hazard a guess, I would say that the Windows build procedure had to go this way because the binaries released on the tcc downloads page cannot know which directory they will eventually occupy. However, in the conventional ./configure && make && make install, you know where the binary is going to live at compile time, so I imagine it's just built into the system there. The configure-based install could probably be revised to be portable.
I would hypothesize that tcc you built at work was built with the unixish approach? ./cofigure, make, make install?