From e.g. a cmd prompt, Windows doesn't like the in-place GHCs:

C:\>C:\cygwin\home\ian\ghc\6.6-branch\build\compiler\stage2\ghc-inplace
'C:\cygwin\home\ian\ghc\6.6-branch\build\compiler\stage2\ghc-inplace' is not recognized as an internal or external command, operable program or batch file.

C:\>cat C:\cygwin\home\ian\ghc\6.6-branch\build\compiler\stage2\ghc-inplace
#!/bin/sh
exec C:/cygwin/home/ian/ghc/6.6-branch/build/compiler/stage2/ghc -BC:\\\\cygwin\\\\home\\\\ian\\\\ghc\\\\6.6-branch\\\\build "$@"

which means the cabal01 test fails thus:

$ ./setup configure --prefix=`pwd`/install --with-compiler=C:/cygwin/home/ian/ghc/6.6-branch/build/compiler/stage1/ghc-inplace --with-hc-pkg=../../../../../utils/ghc-pkg/ghc-pkg-inplace --enable-library-profiling
setup.exe: Warning: Package is copyright All Rights Reserved
setup.exe: Warning: No license-file field.
'C:\cygwin\home\ian\ghc\6.6-branch\build\compiler\stage1\ghc-inplace' is not recognized as an internal or external command,
operable program or batch file.
Configuring test-1.0...

(the odd output order is due to buffering)