I copied guile-gcrypt
I changed all the occurrrences of "gcrypt" in "freexl" in all the relevant files
I created an env with
~/projects/guile-freexl$ guix environment -l ./guix.scm --ad-hoc guile freexl
I run configure and I got
checking for libfreexl-config... no
checking libfreexl's library directory...
checking for libfreexl shared library name... libfreexl
checking whether libfreexl can be dynamically loaded... no
configure: error: GNU libfreexl does not appear to be usable; see `--with-libfreexl-prefix' and `README'.