HP "flavor" of Unix. Notice that, in 2005, HP also owns {Ultrix,OSF/1,Digital Unix,Tru64 Unix}, NonStop, ..., sort-of supports Alpha Linux, ...
"... if you want to compile it and are using the HP-UX C-Compiler you have to adjust your Makefile a bit after running configure.
Change the line
CFLAGS_OPTIMIZE = -O
in
CFLAGS_OPTIMIZE = -O -Ae -DUNIX -DBIT32 -DANSI
and it will compile smoothly."