Terraform was written under Linux (or GNU/Linux if you're an RMS faithful) and should run under any UNIX type system that has the proper libraries and compilers installed. The following are a list of systems that I know terraform has successfully been compiled under
Linux ix86 Debian 2.1 glibc
Linux ix86 Mandrake 6.0 glibc (using pgcc-2.91.66, gcc-2.95)
Linux ix86 Mandrake 6.1 glibc (using pgcc-2.91.66, gcc-2.95)
Linux ix86 Redhat 5.2 glibc (using egcs-2.91.57)
Linux ix86 Redhat 6.0 glibc (using egcs-2.91.66)
Solaris Sparc 2.6 (using egcs 2.91.66)
Solaris Sparc 2.7 (using gcc 2.8.1)
The compiler versions given above are intended as a reference point for a particular platform and the accompanying compiler. Other compiler versions of both gcc and egcs may work just as well or even better, especially if the version is higher than what's listed above. The configure scripts checks wether your system has all required libraries installed and wether your compiler supports all required ANSI C++ features.