added %option ignore_unused to suppress warnings about unused vars and subs in that module/block.

Also improved error for invalid directive.

codeGenIntermediate/src/prog8/codegen/intermediate/IRCodeGen.kt

@@ -1667,6 +1667,7 @@ class IRCodeGen(
                 block.options.forceOutput,
                 block.options.noSymbolPrefixing,
                 block.options.veraFxMuls,
+                block.options.ignoreUnused,
                 translate(block.options.alignment)
             ), block.position)
         for (child in block.children) {

codeGenIntermediate/src/prog8/codegen/intermediate/IRUnusedCodeRemover.kt

@@ -1,7 +1,6 @@
 package prog8.codegen.intermediate
 
 import prog8.code.core.IErrorReporter
-import prog8.code.core.SourceCode.Companion.LIBRARYFILEPREFIX
 import prog8.intermediate.*
 
 
@@ -61,7 +60,7 @@ class IRUnusedCodeRemover(
         irprog.blocks.forEach { block ->
             block.children.filterIsInstance<IRSubroutine>().reversed().forEach { sub ->
                 if(sub.isEmpty()) {
-                    if(!sub.position.file.startsWith(LIBRARYFILEPREFIX)) {
+                    if(!block.options.ignoreUnused) {
                         errors.warn("unused subroutine '${sub.label}'", sub.position)
                     }
                     block.children.remove(sub)
@@ -82,7 +81,7 @@ class IRUnusedCodeRemover(
         irprog.blocks.forEach { block ->
             block.children.filterIsInstance<IRAsmSubroutine>().reversed().forEach { sub ->
                 if(sub.isEmpty()) {
-                    if(!sub.position.file.startsWith(LIBRARYFILEPREFIX)) {
+                    if(!block.options.ignoreUnused) {
                         errors.warn("unused subroutine '${sub.label}'", sub.position)
                     }
                     block.children.remove(sub)