all: remove LLVM 14 support

This is a big change: apart from removing LLVM 14 it also removes typed
pointer support (which was only fully supported in LLVM up to version
14). This removes about 200 lines of code, but more importantly removes
a ton of special cases for LLVM 14.

compiler/calls.go

@@ -45,7 +45,7 @@ func (b *builder) createRuntimeCallCommon(fnName string, args []llvm.Value, name
 	if llvmFn.IsNil() {
 		panic("trying to call non-existent function: " + fn.RelString(nil))
 	}
-	args = append(args, llvm.Undef(b.i8ptrType)) // unused context parameter
+	args = append(args, llvm.Undef(b.dataPtrType)) // unused context parameter
 	if isInvoke {
 		return b.createInvoke(fnType, llvmFn, args, name)
 	}