in reply to installing GD.pm
"Anyone seen this before?"
Up until recently, I would have said no. But recently (1067745), and another (node ID unknown) only 2 days prior, also was related to the problem you indicate your facing. Given the output you've provided. It appears the I isn't being properly populated in make, or configure. Given that it assumes / for gd.h. I'd also be looking at PERFIX; as in PERFIX= /usr, or /usr/local. While it's easy to say it's the install(er). I wouldn't jump to any conclusions.
I'd need to have it in front of me to properly diagnose it (I'm on *BSD). But if you have the ability. You might try configureconfigure --help, or configureconfigure -h, for any clues it may provide.
UPDATE: provided links for Debian's configure
See also: autoconf
¡λɐp ʇɑəɹ⅁ ɐ əʌɐɥ puɐ ʻꜱdləɥ ꜱᴉɥʇ ədoH