On OpenBSD 5.5 compilation of current HEAD fails with:

inplace/bin/deriveConstants --gen-header -o includes/dist-derivedconstants/header/DerivedConstants.h --tmpdir includes/dist-derivedconstants/header/ --gcc-program "/usr/bin/gcc" --gcc-flag -fno-stack-protector --gcc-flag -Iincludes --gcc-flag -Iincludes/dist --gcc-flag -Iincludes/dist-derivedconstants/header --gcc-flag -Iincludes/dist-ghcconstants/header --gcc-flag -Irts --gcc-flag -fcommon --nm-program "/usr/bin/nm"
nm: unknown option -- P
usage: nm [-aCegnoprsuw] [file ...]
deriveConstants: readProcess: /usr/bin/nm "-P" "includes/dist-derivedconstants/header/tmp.o" (exit 1): failed
includes/ghc.mk:167: recipe for target 'includes/dist-derivedconstants/header/DerivedConstants.h' failed
gmake[1]: *** [includes/dist-derivedconstants/header/DerivedConstants.h] Error 1
Makefile:71: recipe for target 'all' failed
gmake: *** [all] Error 2

This is due to OpenBSD's nm not supporting the -P option.

Perhaps it can be fixed by using 'objdump --syms' instead of 'nm -P' (see attached OpenBSD-only patch).