Guile 2.9.9, like .8 and .7, does not build on Cygwin (64 bit). Configure runs without error, but make crashes with this (truncated to just the tail):
Making all in bootstrap
make: Entering directory '/cygdrive/c/Users/rr828893/Downloads/guile-2.9.9/bootstrap'
BOOTSTRAP GUILEC ice-9/eval.go
BOOTSTRAP GUILEC ice-9/psyntax-pp.go
BOOTSTRAP GUILEC language/cps/intmap.go
BOOTSTRAP GUILEC language/cps/intset.go
BOOTSTRAP GUILEC language/cps/graphs.go
BOOTSTRAP GUILEC ice-9/vlist.go
BOOTSTRAP GUILEC srfi/srfi-1.go
/bin/sh: line 6: 4294 Segmentation fault (core dumped) GUILE_AUTO_COMPILE=0 ../meta/build-env guild compile --target="x86_64-unknown-cygwin" -O1 -Oresolve-primitives -L "/home/rr828893/Downloads/guile-2.9.9/module" -L "/home/rr828893/Downloads/guile-2.9.9/guile-readline" -o "srfi/srfi-1.go" "../module/srfi/srfi-1.scm"
make: *** [Makefile:1930: srfi/srfi-1.go] Error 139
make: Leaving directory '/cygdrive/c/Users/rr828893/Downloads/guile-2.9.9/bootstrap'
make: *** [Makefile:1849: all-recursive] Error 1
make: Leaving directory '/cygdrive/c/Users/rr828893/Downloads/guile-2.9.9'
make: *** [Makefile:1735: all] Error 2
All previous problems (which were easy to work around) have gone away in this release, which is progress, but it doesn't get me past Guile 2.2.