bug#72693: openscad-2021.01 build failure

[bdju]

build log here: https://0x0.st/X4Rv.txt

```
building /gnu/store/7fc94ifad3hc5i1vvvm8vkq80bvqfn7x-openscad-2021.01.drv...
\ 'build' phase��@ build-log 21141 217
��op1’ [-Wunused-parameter]
  773 |   template <typename T, typename U> Value operator()(const T &op1, 
const U &op2) const { return false; }
      |                                                      ~~~~~~~~~^~~
| 'build' phasebuilder for 
`/gnu/store/7fc94ifad3hc5i1vvvm8vkq80bvqfn7x-openscad-2021.01.drv' failed with 
exit code 1
build of /gnu/store/7fc94ifad3hc5i1vvvm8vkq80bvqfn7x-openscad-2021.01.drv failed
View build log at 
'/var/log/guix/drvs/7f/c94ifad3hc5i1vvvm8vkq80bvqfn7x-openscad-2021.01.drv.gz'.
guix package: error: build of 
`/gnu/store/7fc94ifad3hc5i1vvvm8vkq80bvqfn7x-openscad-2021.01.drv' failed
guix package --upgrade . --do-not-upgrade={pfetch,rgbds}  852.41s user 4.31s 
system 37% cpu 38:13.46 total
```

guix version: guix (GNU Guix) 6c045f2c9eb7b8efe7c8a1002cda990abaa9be1a
***I am using Guix System.***