A multilib package can be installed simultaneously in 32 and 64 bits versions. In linux, multilib can be summarized as only architecture independent files in /usr/include and architecture dependent files in /usr/lib and /usr/lib64 (this is the layout in fedora, in other distributions it differs).
Blitz has an architecture dependent file in /usr/include, the header bzconfig.h
This file is created at build time and depends on the architecture.
As a workaround for the fedora package I have moved the bzconfig.h file to libdir/blitz/include and modified the blitz.pc file so that this new directory is included.
Another solution could be to provide a set of predefined bzconfig. files in /usr/include (one per arch) and to decide which one to load at compile time.
Migrated from: https://sourceforge.net/p/blitz/bugs/18/
As reported by @sergiopasra on 2008-11-13: