It's impossible to buy an x86 computer nowadays. A lateish version of gcc warns about usages of TOSTRING in statement.c. The reason is well-documented in a comment in that file, Brandy assumes pointers are 32 bits wide.
It's no great hardship to pass "-m32" to the C compiler so possibly not even worth fixing, but I thought this Feature Request would be a good way to show packagers why they need to do so (e.g. the packaged NetBSD version of brandy is 64-bit).
This is now fixed in version 1.20.1