### Please describe the problem.

Git-annex commit 7550ef9a2 doesn't compile on Windows without a small patch.

### What steps will reproduce the problem?

`stack setup && stack build`

### What version of git-annex are you using? On what operating system?

[[!format sh """
git-annex version: 8.20210804-g7550ef9a2
build flags: Assistant Webapp Pairing TorrentParser Feeds Testsuite S3 WebDAV
dependency versions: aws-0.22 bloomfilter-2.0.1.0 cryptonite-0.26 DAV-1.3.4 feed-1.3.0.1 ghc-8.8.4 http-client-0.6.4.1 persistent-sqlite-2.10.6.2 torrent-10000.1.1 uuid-1.3.13 yesod-1.6.1.0
key/value backends: SHA256E SHA256 SHA512E SHA512 SHA224E SHA224 SHA384E SHA384 SHA3_256E SHA3_256 SHA3_512E SHA3_512 SHA3_224E SHA3_224 SHA3_384E SHA3_384 SKEIN256E SKEIN256 SKEIN512E SKEIN512 BLAKE2B256E BLAKE2B256 BLAKE2B512E BLAKE2B512 BLAKE2B160E BLAKE2B160 BLAKE2B224E BLAKE2B224 BLAKE2B384E BLAKE2B384 BLAKE2BP512E BLAKE2BP512 BLAKE2S256E BLAKE2S256 BLAKE2S160E BLAKE2S160 BLAKE2S224E BLAKE2S224 BLAKE2SP256E BLAKE2SP256 BLAKE2SP224E BLAKE2SP224 SHA1E SHA1 MD5E MD5 WORM URL X*
remote types: git gcrypt p2p S3 bup directory rsync web bittorrent webdav adb tahoe glacier ddar git-lfs httpalso borg hook external
operating system: mingw32 x86_64
supported repository versions: 8
upgrade supported from repository versions: 2 3 4 5 6 7
"""]]

Windows version 21H1 (build 19043.1165), 64 bit.

### Please provide any additional information below.

Relevant parts of the build log:

[[!format sh """
jkniiv@AINESIS MINGW64 /c/annx
$ tail -n 25 /c/Projektit/git-annex.branchable.com/git-annex--BUILD-210813-7550ef9a2/stack.build.LOG~102
[333 of 665] Compiling Annex.Content.LowLevel
[334 of 665] Compiling Annex.Content.PointerFile
[335 of 665] Compiling Annex.ChangedRefs
[336 of 665] Compiling RemoteDaemon.Types
[337 of 665] Compiling Assistant.Types.RemoteControl
[338 of 665] Compiling RemoteDaemon.Transport.Ssh.Types
[339 of 665] Compiling P2P.Protocol
[340 of 665] Compiling P2P.IO
[341 of 665] Compiling CmdLine.GitRemoteTorAnnex
[342 of 665] Compiling Annex.CheckIgnore
[343 of 665] Compiling Annex.CheckAttr
[344 of 665] Compiling Backend
[345 of 665] Compiling Annex.Verify

Annex\Verify.hs:151:50: error:
    Not in scope: type constructor or class `TMVar'
    |
151 | tailVerify :: IncrementalVerifier -> FilePath -> TMVar () -> IO Bool

    |                                                  ^^^^^


--  While building package git-annex-8.20210803 (scroll up to its section to see the error) using:
      C:\Users\jkniiv\Projektit\git-annex.branchable.com\git-annex--BUILD-210813-7550ef9a2\.stack-work\dist\29cc6475\setup\setup --builddir=.stack-work\dist\29cc6475 build exe:git-annex --ghc-options " -fdiagnostics-color=always"
    Process exited with code: ExitFailure 1

# End of transcript.
"""]]

The change I made was the following:

[[!format diff """
diff --git a/Annex/Verify.hs b/Annex/Verify.hs
index 39ef45981..f43e20db1 100644
--- a/Annex/Verify.hs
+++ b/Annex/Verify.hs
@@ -36,6 +36,8 @@ import Types.Key
 import qualified System.INotify as INotify
 import Control.Concurrent.STM
 import qualified Data.ByteString as S
+#else
+import Control.Concurrent.STM
 #endif

 data VerifyConfig = AlwaysVerify | NoVerify | RemoteVerify Remote | DefaultVerify
"""]]

This then compiled cleanly and completed the test suite ok.

### Have you had any luck using git-annex before? (Sometimes we get tired of reading bug reports all day and a lil' positive end note does wonders)

Git Annex is great. It works with multi-gigabyte backup files (largest around 180GB) via the BLAKE2B160E backend just dandy :)

> [[fixed|done]] --[[Joey]]
