ClassfileParser: correct types for annotation arguments

As specified in https://docs.oracle.com/javase/specs/jvms/se8/html/jvms-4.html#jvms-4.7.16.1,
an annotation argument of type boolean, byte, char or short will be represented
as a CONSTANT_Integer in the classfile, so when we parse it we get an
Int, but before this commit we did not convert this Int to the correct
type for the annotation argument, thus creating ill-typed trees.

Author: smarter

compiler/src/dotty/tools/dotc/core/classfile/ClassfileParser.scala

@@ -430,8 +430,9 @@ class ClassfileParser(
     tag match {
       case STRING_TAG =>
         if (skip) None else Some(Literal(Constant(pool.getName(index).toString)))
-      case BOOL_TAG | BYTE_TAG | CHAR_TAG | SHORT_TAG | INT_TAG |
-        LONG_TAG | FLOAT_TAG | DOUBLE_TAG =>
+      case BOOL_TAG | BYTE_TAG | CHAR_TAG | SHORT_TAG =>
+        if (skip) None else Some(Literal(pool.getConstant(index, tag)))
+      case INT_TAG | LONG_TAG | FLOAT_TAG | DOUBLE_TAG =>
         if (skip) None else Some(Literal(pool.getConstant(index)))
       case CLASS_TAG =>
         if (skip) None else Some(Literal(Constant(pool.getType(index))))
@@ -829,7 +830,7 @@ class ClassfileParser(
             if (sym == classRoot.symbol) staticScope.lookup(name)
             else {
               var module = sym.companionModule
-              if (module == NoSymbol && sym.isAbsent)
+              if (!module.exists && sym.isAbsent)
                 module = sym.scalacLinkedClass
               module.info.member(name).symbol
             }
@@ -1045,14 +1046,28 @@ class ClassfileParser(
       getClassSymbol(index)
     }
 
-    def getConstant(index: Int)(implicit ctx: Context): Constant = {
+    def getConstant(index: Int, tag: Int = -1)(implicit ctx: Context): Constant = {
       if (index <= 0 || len <= index) errorBadIndex(index)
       var value = values(index)
       if (value eq null) {
         val start = starts(index)
         value = (in.buf(start).toInt: @switch) match {
           case CONSTANT_STRING =>
             Constant(getName(in.getChar(start + 1).toInt).toString)
+          case CONSTANT_INTEGER if tag != -1 =>
+            val value = in.getInt(start + 1)
+            (tag: @switch) match {
+              case BOOL_TAG =>
+                Constant(value != 0)
+              case BYTE_TAG =>
+                Constant(value.toByte)
+              case CHAR_TAG =>
+                Constant(value.toChar)
+              case SHORT_TAG =>
+                Constant(value.toShort)
+              case _ =>
+                errorBadTag(tag)
+            }
           case CONSTANT_INTEGER =>
             Constant(in.getInt(start + 1))
           case CONSTANT_FLOAT =>