Perf builds of HEAD seem broken on Windows

When building HEAD (currently at ed37027f) with a perf flavour with Hadrian on Windows, I seem to obtain a completely broken GHC.

git clean -xfd
./boot && ./configure --enable-tarballs-autodownload
hadrian/build.bat -j --flavour=perf

I get a GHC that seems unable to do anything. ghc --version stalls for a bit and then returns silently, same with ghci. ghc-pkg segfaults:

$ "_build/stage1/bin/ghc-pkg.exe"

Access violation in generated code when executing data at 0x7ff75be6dd58

 Attempting to reconstruct a stack trace...

   Frame        Code address
 * 0xdc9c57d8f0 0x7ff75be6dd58 C:\Haskell\ghc\master\_build\stage1\bin\ghc-pkg.exe+0x33fdd58
 * 0xdc9c57d8f8 0xffffffffffffffff
 * 0xdc9c57d900 0x2be00000052
 * 0xdc9c57d908 0x500000001
 * 0xdc9c57d910 0xdc9c57e3f0

Trying to run the test-suite fails with the error

Exception: Command failed: ['"C:/Haskell/ghc/primops/_build/stage1/bin/ghc-pkg.exe"', 'dump']

presumably because ghc-pkg segfaults.

Development flavours seem to not be affected; I've been building devel2 ghcs without issue.