For what it's worth I was able to successfully build a 64-bit version of
GEMPAK7 on Solaris 11 x64 using Solaris Studio 12.2 by using -xarch=generic64
in Makeinc.x86 and by adding 'CFLAGS=-xarch=generic64' to some of the configure
lines in some of the Makefiles in extlibs.
Unfortunately, the resulting program is broken in many ways. NSHARP won't
display Observed Soundings and selecting Model Data won't evenin get you a list
of available times. Sat, radar, obs, works fine in NMAP2 but trying to display
Model Data results in a crash. gdpoint doesn't work at all, gdplot2 conversely
works fine..so it's a mixed bag.
If someone else decides to try this and gets it to work I'd like to hear about
it, even if you used gcc. I am going to move on and just keep working around
the 2GB file size limit.