Hello,
I guess I'm just really unlucky. Compilation of "required merge" according to
git bisect fails with:

CXXLD    libOSMesa.la
/usr/bin/ld: i386:x86-64 architecture of input file
`../../../../src/mesa/.libs/libmesa.a(ast_expr.o)' is incompatible with i386
output

Which is similar to a bug report here: bug 50754. Adding those variables into
the build script doesn't help (in fact, they've been in before). Looks like I'm
stuffed yet again!