all: use the new LLVM pass manager

The old LLVM pass manager is deprecated and should not be used anymore.
Moreover, the pass manager builder (which we used to set up a pass
pipeline) is actually removed from LLVM entirely in LLVM 17:
https://reviews.llvm.org/D145387
https://reviews.llvm.org/D145835

The new pass manager does change the binary size in many cases: both
growing and shrinking it. However, on average the binary size remains
more or less the same.

This is needed as a preparation for LLVM 17.

interp/interp_test.go

@@ -77,12 +77,9 @@ func runTest(t *testing.T, pathPrefix string) {
 	}
 
 	// Run some cleanup passes to get easy-to-read outputs.
-	pm := llvm.NewPassManager()
-	defer pm.Dispose()
-	pm.AddGlobalOptimizerPass()
-	pm.AddDeadStoreEliminationPass()
-	pm.AddAggressiveDCEPass()
-	pm.Run(mod)
+	to := llvm.NewPassBuilderOptions()
+	defer to.Dispose()
+	mod.RunPasses("globalopt,dse,adce", llvm.TargetMachine{}, to)
 
 	// Read the expected output IR.
 	out, err := os.ReadFile(pathPrefix + ".out.ll")