This conflict with the DJGPP libc which includes a pow2 function¹

We cannot make DJGPP POSIX only (using -D_POSIX_SOURCE) to avoid this
kind of symbols conflicts due to the lack of both posix_memalign and
memalign (DJGPP non standard function) in that POSIX mode. We currently
rely on memalign for aligned heap allocation.

[1]: http://www.delorie.com/djgpp/doc/libc-2.02/libc_536.html