"Failed to remove" errors during Windows build from hsc2hs

The Windows build over here spews a bunch of errors during the build like the ones below. All of them seem to be related to hsc2hs. The errors do not break the build for some reason, so the problem is not critical, but we should look into what's going on here.

Note that the errors are indeterministic and the set of files affected varies between builds.

Examples:

ghctrace.2/3.log:Failed to remove file libraries/base/dist-install/build/System/CPUTime_hsc_make.exe; error= DeleteFile "libraries/base/dist-install/build/System/CPUTime_hsc_make.exe": permission denied (Access is denied.)
ghctrace.2/4.log:Failed to remove file libraries/hpc/dist-boot/build/Trace/Hpc/Reflect_hsc_make.exe; error= DeleteFile "libraries/hpc/dist-boot/build/Trace/Hpc/Reflect_hsc_make.exe": permission denied (Access is denied.)
ghctrace.2/4.log:Failed to remove file compiler/stage2/build/Fingerprint_hsc_make.exe; error= DeleteFile "compiler/stage2/build/Fingerprint_hsc_make.exe": permission denied (Access is denied.)
ghctrace.3/1.log:Failed to remove file libraries/hpc/dist-boot/build/Trace/Hpc/Reflect_hsc_make.exe; error= DeleteFile "libraries/hpc/dist-boot/build/Trace/Hpc/Reflect_hsc_make.exe": permission denied (Access is denied.)
ghctrace.3/4.log:Failed to remove file libraries/old-time/dist-install/build/System/Time_hsc_make.exe; error= DeleteFile "libraries/old-time/dist-install/build/System/Time_hsc_make.exe": permission denied (Access is denied.)
ghctrace.3/5.log:Failed to remove file libraries/Win32/dist-install/build/Graphics/Win32/GDI/Pen_hsc_make.exe; error= DeleteFile "libraries/Win32/dist-install/build/Graphics/Win32/GDI/Pen_hsc_make.exe": permission denied (Access is denied.)