As discussed on IRC, it turns out no world rebuild happens:

$ ./pre-inst-env guix build --system=x86_64-linux -d --no-grafts
texlive-bin texlive-latex-base libelf bdb sed hello gcc-toolchain
/gnu/store/9f3vsmg2c9qa91r1dlffbnpr0kbzpvxy-gcc-toolchain-10.2.0.drv
/gnu/store/sihk9hiiqhqkckjs4dzl2vdk5dfv2923-hello-2.10.drv
/gnu/store/kmpw9qv3pdc31q3b3mnsr8ypqkcd4q95-sed-4.8.drv
/gnu/store/2vq0yvhrn6mk2lr40mabhnx6r0pdrccn-bdb-6.2.32.drv
/gnu/store/mj1q7a8x4hv2c5n1xqnakxhsf5fny609-libelf-0.8.13.drv
/gnu/store/qhnf8nqblgz22id4fzn2bb94mbdzghpk-texlive-latex-base-
51265.drv
/gnu/store/pwhz1k213dd8bsc9sq85vds1cqjwc1by-texlive-bin-20190410.drv

With commit 16cc8f8851ee38dfaa74ef976b0609a837ba682d (current wip-
ppc64le-for-master) which includes those patches AIUI.