Don't reuse Compiler from ScriptEnv0 to determine the TestCompiler

In the testsuite we generate a module `ScriptEnv0.hs` which records information about the compiler used to build the testsuite, the packages etc so that the test runner can then use this information to

However, this is very fragile because

* `ScriptEnv0.hs` is generated by a module compiled against `Cabal-3.10`
* The file is compiled against `Cabal-3.11`

So if any definition changes between 3.10 and 3.11 then the new version will fail to read the generated file.

Really we should record the information which needs to be persisted in a more generic way (ie only depending on `base`) so that you can be sure the serialisation/deserialisation will work.

This seems to have worked for a while because these data types never change.. but now `compilerAbiTag` is populated by `3.11` but not by `3.10`, which leads to bugs like haskell#9725

See haskell#9730

Author: mpickering

cabal-testsuite/src/Test/Cabal/Monad.hs

@@ -248,10 +248,12 @@ runTestM mode m = withSystemTempDirectory "cabal-testsuite" $ \tmp_dir -> do
     -- Reconfigure according to user flags
     let cargs = testCommonArgs args
 
+    let ghc_path = case argGhcPath cargs of
+                    Just p -> p
+                    Nothing -> programPath (fromJust $ lookupProgram ghcProgram program_db0)
+
     -- Reconfigure GHC
-    (comp, platform, program_db2) <- case argGhcPath cargs of
-        Nothing -> return (runnerCompiler senv, runnerPlatform senv, program_db0)
-        Just ghc_path -> do
+    (comp, platform, program_db2) <- do
             -- All the things that get updated paths from
             -- configCompilerEx.  The point is to make sure
             -- we reconfigure these when we need them.