kernel v5.9-rc6 not compiling

[bob]

Hi.  I've been building kernels weekly since 1996.  Never had one not 
build before today.  v5.9-rc6 does not compile.

Error:

  AR      drivers/gpu/built-in.a
make: *** [Makefile:1784: drivers] Error 2
  CALL    scripts/checksyscalls.sh
  CALL    scripts/atomic/check-atomics.sh
  DESCEND  objtool
  CHK     include/generated/compile.h
  CC      drivers/dax/super.o
drivers/dax/super.c:325:6: error: redefinition of ‘dax_supported’
  325 | bool dax_supported(struct dax_device *dax_dev, struct 
block_device *bdev,
      |      ^~~~~~~~~~~~~
In file included from drivers/dax/super.c:16:
./include/linux/dax.h:162:20: note: previous definition of 
‘dax_supported’ was here
  162 | static inline bool dax_supported(struct dax_device *dax_dev,
      |                    ^~~~~~~~~~~~~
make[2]: *** [scripts/Makefile.build:283: drivers/dax/super.o] Error 1
make[1]: *** [scripts/Makefile.build:500: drivers/dax] Error 2
make: *** [Makefile:1784: drivers] Error 2
sed: can't read modules.order: No such file or directory
make: *** [Makefile:1416: _modinst_] Error 2
sh ./arch/x86/boot/install.sh 5.9.0-rc6 arch/x86/boot/bzImage \
    System.map "/boot"

 *** Missing file: arch/x86/boot/bzImage
 *** You need to run "make" before "make install".

make[1]: *** [arch/x86/boot/Makefile:160: install] Error 1
make: *** [arch/x86/Makefile:274: install] Error 2
You may need to edit your /etc/default/grub file


... so its not like I'm stuck, I can pick any of a number of old kernels 
from the bootloader.  And I've had a lot of rc kernels over the years 
that would build, but weren't finished (occasionally I would get an oops 
in dmesg).  Again pick another kernel from the bootloader, preferrably a 
more stable non-rc one. But I don't think I've ever had a kernel not 
compile before.  I'm waiting for the nouveau drivers to firm up, but DAX 
is page cache for ext2/3/4 file systems (and I use ext4).  Hopefully my 
report is useful.  Thank you.