"Thread-local storage not supported" for Mac

On a fresh clone of HEAD, building eventually gets me

"inplace/bin/ghc-stage1" -optc-Wall -optc-Wextra -optc-Wstrict-prototypes -optc-Wmissing-prototypes -optc-Wmissing-declarations -optc-Winline -optc-Waggregate-return -optc-Wpointer-arith -optc-Wmissing-noreturn -optc-Wnested-externs -optc-Wredundant-decls -optc-Iincludes -optc-Iincludes/dist -optc-Iincludes/dist-derivedconstants/header -optc-Iincludes/dist-ghcconstants/header -optc-Irts -optc-Irts/dist/build -optc-DCOMPILING_RTS -optc-fno-strict-aliasing -optc-fno-common -optc-DDTRACE -optc-O2 -optc-fomit-frame-pointer -optc-DRtsWay=\"rts_thr\" -optc-funroll-loops -static -optc-DTHREADED_RTS  -H64m -O -fasm -Iincludes -Iincludes/dist -Iincludes/dist-derivedconstants/header -Iincludes/dist-ghcconstants/header -Irts -Irts/dist/build -DCOMPILING_RTS -package-name rts -dcmm-lint  -DDTRACE     -i -irts -irts/dist/build -irts/dist/build/autogen -Irts/dist/build -Irts/dist/build/autogen           -O2    -c rts/sm/Evac.c -o rts/dist/build/sm/Evac.thr_o

In file included from rts/sm/Evac.c:21:0: 

rts/sm/GCTDecl.h:71:0:
     error: thread-local storage not supported for this target

I'm on Mac OS 10.8.5, Xcode 4.6.1 (4H512), bootstrapping from 7.6.3, with BuildFlavour = devel2.

With this report, my build is dead in the water.

(Separately, Trac doesn't have an option for reporting a bug in version 7.9!)

Trac metadata

Trac field	Value
Version	7.8.1-rc1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
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Blocking
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