mkmakemod.sh 2nd stage build failure

[Kete <kete@ninthfloor.org>]

Hello,
I am trying to build Zsh for an emerging package manager named Guix, but the build failed at the second stage of mkmakemod.sh when it tried to use /bin/sh. I see I can disable the 2nd stage with an -i option. What are the consequences of disabling the second stage? Here is my error (you might notice Guix is based on Nix):

starting phase `build'
make[1]: Entering directory '/tmp/nix-build-zsh-5.0.2.drv-1/zsh-5.0.4/Src'
cd .. && /nix/store/97vnvqq5daji73b71v4cnmyaa7r3hzk2-bash-4.2/bin/sh $top_srcdir/Src/mkmakemod.sh Src Makemod
creating Src/Makemod.in
Src/../Src/mkmakemod.sh: line 467: /bin/sh: No such file or directory
Makefile:299: recipe for target 'Makemod' failed
make[1]: *** [Makemod] Error 1

Here are lines 464-470 of mkmakemod.sh:

if $second_stage ; then
    trap "rm -f $the_subdir/${the_makefile}; exit 1" 1 2 15

    ${CONFIG_SHELL-/bin/sh} ./config.status \
	--file=$the_subdir/${the_makefile}:$the_subdir/${the_makefile}.in ||
    exit 1
fi