Thank you for the patch, Bruno and the explanation, Sam. I've just pushed the patch with this tweaked commit log:
build: fix broken executable on 32-bit x86 systems with musl libc
* configure.ac (gzip_cv_assembler): Set to no on musl libc.
Thanks to Sam James for the explanation: musl doesn't support TEXTRELs
https://www.openwall.com/lists/musl/2020/09/25/1
Reported in https://bugs.gnu.org/80855
