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.

transform/transform.go

@@ -22,7 +22,7 @@ import (
 // the -opt= compiler flag.
 func AddStandardAttributes(fn llvm.Value, config *compileopts.Config) {
 	ctx := fn.Type().Context()
-	_, sizeLevel, _ := config.OptLevels()
+	_, _, sizeLevel := config.OptLevel()
 	if sizeLevel >= 1 {
 		fn.AddFunctionAttr(ctx.CreateEnumAttribute(llvm.AttributeKindID("optsize"), 0))
 	}