bug#75958: Guile gnulib module missing ffs

[Bug reports for GUILE, GNU's Ubiquitous Extension Language]

Hi, 

I've been trying to build Guile with a mingw-w64-ucrt toolchain and I've come 
across an error, undefined reference to ffs. I believe the current distribution 
of Guile 3.0.10 is missing this in its gnulib modules.

Dane Johnson