Add GHC 9.12 to compatibility matrix

Author: martijnbastiaan

README.md

@@ -77,6 +77,7 @@ Note that release branches might contain non-released patches.
 | 9.6  | &#x2714;&#xfe0f;<sup>3</sup>    | &#x2714;&#xfe0f;<sup>3,4</sup>  | &#x2714;&#xfe0f;<sup>3</sup>    | 1.8              | &#x2714;&#xfe0f;
 | 9.8  | &#x2714;&#xfe0f;                | &#x2714;&#xfe0f;<sup>4</sup>    | &#x2714;&#xfe0f;                | 1.8              | ️&#x2714;&#xfe0f;
 | 9.10 | &#x2714;&#xfe0f;                | &#x2714;&#xfe0f;<sup>4</sup>    | &#x2714;&#xfe0f;                | 1.8              | ️&#x2714;&#xfe0f;
+| 9.12 | &#x2714;&#xfe0f;                | &#x2714;&#xfe0f;<sup>4,5</sup>  | &#x2714;&#xfe0f;<sup>5</sup>    | 1.8.3            | ️&#x2714;&#xfe0f;
 
 
 <sup>1</sup> GHC 9.2 contains a regression, rendering Clash error messages indecipherable. This change was reverted in 9.4.
@@ -85,7 +86,9 @@ Note that release branches might contain non-released patches.
 
 <sup>3</sup> Clash starts extremely slowly when compiled with 9.4.8 up to and including 9.6.2. Consider downgrading to 9.4.7 or upgrading to 9.6.3 and up.
 
-<sup>4</sup> Clash starts extremely slowly on Windows with GHC 9.6 through 9.10, consider downgrading to 9.4.7
+<sup>4</sup> Clash starts extremely slowly on Windows with GHC 9.6 through 9.12, consider downgrading to 9.4.7
+
+<sup>5</sup> We're waiting for Stackage to publish a nightly based on GHC 9.12 in order to get CI working on Windows and macOS.
 
 ## Cabal
 To use Cabal you need both Cabal and GHC installed on your system. We recommend using [ghcup](https://www.haskell.org/ghcup/). For more information, see [https://www.haskell.org/downloads/](https://www.haskell.org/downloads/).