Patching nettle.cmod uncovered a problem. The tarball ships with the cmods precompiled as C code. But by patching nettle.cmod, nettle.c becomes out-of-date:

.cmod.c: $(BUILD_BASE)/precompile.sh-stamp $(TMP_BINDIR)/precompile.pike $(BUILD_BASE)/precompile.sh --cache precompile.pike >"$@" "$<" || { rm "$@"; exit 1; }

But precompile.sh tries to run pike like this:

if [ x"$1" = xprecompile.pike ] ; then if pike -x 2>&1 | grep precompile > /dev/null 2>&1 ; then shift exec pike -x precompile "$@" fi fi

which of course doesn't work if pike isn't already installed.