Saratoga:
Ok, after getting the additional Cygwin packages mentioned in the CrossCompiler documentation and running the git clone, I ran rockboxdev.sh and selected 'a' for arm.
There were many screenfuls of the message "/usr/bin/expr.exe: error while loading shared libraries cyggmp-3.dll: cannot open shared object file: no such file or directory".
Then the compile proceeded for an hour using all 8 cpus with no screen activity, followed by "line 207 1316 segmentation fault".
I found a file D:\cygwin\tmp\rbdev-build\build-binutils\bash.exe.stackdump dated correctly which contains:-
Exception: STATUS_STACK_OVERFLOW at eip=6116F503
eax=0000102C ebx=612AEEC0 ecx=00092EDC edx=00000000 esi=61240180 edi=00001A64
ebp=000A2EE8 esp=000A2ED0 program=D:\cygwin\bin\bash.exe, pid 6756, thread main
cs=0023 ds=002B es=002B fs=0053 gs=002B ss=002B
Stack trace:
.
.
. etc.
I ran it again with the same result.
Saint:
Unfortunately, the rockbox VM image is not compatible with the latest version of Virtualbox. The image has an old version of the virtualbox extension pack loaded. Attempting to upgrade this with the latest gives a failure relating to kernel-source and kernel-syms. Without this upgrade, USB doesn't work.