Checking if your kit is complete...
Looks good
Writing Makefile for Sys::PortIO
cp PortIO.pm blib/lib/Sys/PortIO.pm
AutoSplitting blib/lib/Sys/PortIO.pm (blib/lib/auto/Sys/PortIO)
/export/home/cpanrun/build/5.6.1/bin/perl -I/export/home/cpanrun/build/5.6.1/lib/5.6.1/sun4-solaris-thread-multi -I/export/home/cpanrun/build/5.6.1/lib/5.6.1 /export/home/cpanrun/build/5.6.1/lib/5.6.1/ExtUtils/xsubpp  -typemap /export/home/cpanrun/build/5.6.1/lib/5.6.1/ExtUtils/typemap PortIO.xs > PortIO.xsc && mv PortIO.xsc PortIO.c
Please specify prototyping behavior for PortIO.xs (see perlxs manual)
gcc -c  -DUSE_REENTRANT_API -D_POSIX_PTHREAD_SEMANTICS -D_REENTRANT -fno-strict-aliasing -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64 -O2   -DVERSION=\"0.1\" -DXS_VERSION=\"0.1\" -fPIC -I/export/home/cpanrun/build/5.6.1/lib/5.6.1/sun4-solaris-thread-multi/CORE  PortIO.c
PortIO.xs:47: sys/io.h: No such file or directory
make: *** [PortIO.o] Error 1