As originally discussed in upstream bug report 44684, any package
bootstrapped using the upstream libtool.m4 will fail to recognise
macOS BigSur and use the wrong linker flags, which could result in
issues when the libraries are later dlopen (ex: libgcrypt when used by
Guile 3.0.7 through guile-gcrypt[2])

A partial fix for this was committed as
debian/patches/0070-libtool-bigsur.patch but it only corrected the
default call, and will break if MACOSX_DEPLOYMENT_TARGET=12.0 is
provided (which will happen with the release of Monterrey next week)

The simplest solution would be to change the last condition to match
all versions instead of only "10.*|11.*"

[1] https://debbugs.gnu.org/cgi/bugreport.cgi?bug=44684
[2] https://dev.gnupg.org/T5610