[ 4 of 11] Compiling Reflex.Dom.Internal ( src\Reflex\Dom\Internal.hs, dist\build\Reflex\Dom\Internal.o )
ghc.exe: internal error: checkProddableBlock: invalid fixup in runtime linker: 00000000184b3978
    (GHC version 7.10.1 for x86_64_unknown_mingw32)
    Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug

This happens with unmodified reflex-dom.cabal (which specifies -funbox-strict-fields and -O2) and also with all ghc-options: flags removed and -O or -O0. When compiling with the bundled mingw it also pops up a GUI error window:

ghc.exe - Entry Point Not Found

The procedure entry point pthread_cond_timedwait_relative_np could not be located in the dynamic link library libwinpthread-1.dll.

I also tried using a fully-updated mingw64 from MSYS2, which has solved -pthread issues for me in the past, but that simply crashes with no additional message.

Verbose cabal output attached.