Windows breakage -- again

[Simon Peyton Jones]

Aargh!  The Windows build has broken - again.  I can't build GHC on my laptop any more.
A clean 'sh validate' finishes as below.  What on earth is `___sync_fetch_and_add_1'?
Can anyone help?  Thanks!
Simon

"inplace/bin/ghc-stage2.exe" -hisuf hi -osuf  o -hcsuf hc -static  -H32m -O -Werror -Wall -H64m -O0    -package-name vector-0.10.9.1 -hide-all-packages -i -ilibraries/vector/. -ilibraries/vector/dist-install/build -ilibraries/vector/dist-install/build/autogen -Ilibraries/vector/dist-install/build -Ilibraries/vector/dist-install/build/autogen -Ilibraries/vector/include -Ilibraries/vector/internal   -optP-DVECTOR_BOUNDS_CHECKS -optP-include -optPlibraries/vector/dist-install/build/autogen/cabal_macros.h -package base-4.7.1.0 -package deepseq-1.3.0.2 -package ghc-prim-0.3.1.0 -package primitive-0.5.2.1 -O2 -XHaskell98 -XCPP -XDeriveDataTypeable -O2 -O -dcore-lint -fno-warn-deprecated-flags  -no-user-package-db -rtsopts -Wwarn     -odir libraries/vector/dist-install/build -hidir libraries/vector/dist-install/build -stubdir libraries/vector/dist-install/build   -c libraries/vector/./Data/Vector/Fusion/Stream/Monadic.hs -o libraries/vector/dist-install/build/Data/Vector/Fusion/Stream/Monadic.o

Loading package ghc-prim ... linking ... ghc-stage2.exe: unable to load package `ghc-prim'

ghc-stage2.exe: C:\code\HEAD\libraries\ghc-prim\dist-install\build\HSghc-prim-0.3.1.0.o: unknown symbol `___sync_fetch_and_add_1'

libraries/vector/ghc.mk:5: recipe for target 'libraries/vector/dist-install/build/Data/Vector/Fusion/Stream/Monadic.o' failed

make[1]: *** [libraries/vector/dist-install/build/Data/Vector/Fusion/Stream/Monadic.o] Error 1

I
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