On Windows (sigh).  Seems to be due to Simon Marlow’s 2a6f193b

rts\Schedule.c: In function 'suspendThread':

rts\Schedule.c:2239:3:

     error: expected ';' before 'EnterCriticalSection'

rts/ghc.mk:236: recipe for target 'rts/dist/build/Schedule.thr_o' failed