And considering the definition of system(3) in glibc:
@ sysdeps/posix/system.c (took me way too long to find this; glibc's
source code is a maze ;))
```
#define SHELL_PATH "/bin/sh" /* Path of the shell. */
#define SHELL_NAME "sh" /* Name to give it. */
```
couldn't we just use `-DSHELL_PATH=/gnu/store/...`?
-- (
