HEAD doesn't build. Totally stalled.

[Simon Peyton Jones]

I'm getting this failure in a clean HEAD build. Any ideas?    I'm totally stalled because I can't build GHC any more.
I'm using Windows Subsystem for Linux (WSL).
Help help!
Thanks
Simon

/home/simonpj/code/HEAD-9/rts/dist/build/libHSrts_thr_p.a(RtsSymbols.thr_p_o): RtsSymbols.c:rtsSyms: error: undefined reference to '__stack_chk_guard'

collect2: error: ld returned 1 exit status

`cc' failed in phase `Linker'. (Exit code: 1)

utils/iserv/ghc.mk:105: recipe for target 'utils/iserv/stage2_p/build/tmp/ghc-iserv-prof' failed

make[1]: *** [utils/iserv/stage2_p/build/tmp/ghc-iserv-prof] Error 1

make[1]: *** Waiting for unfinished jobs....
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.haskell.org/pipermail/ghc-devs/attachments/20200714/8122729a/attachment.html>