findbugs fixes

com.oracle.truffle.r.runtime/src/com/oracle/truffle/r/runtime/Utils.java

@@ -194,7 +194,7 @@ public final class Utils {
         }
     }
 
-    private static Charset UTF8;
+    private static volatile Charset UTF8;
 
     public static Charset getUTF8() {
         if (UTF8 == null) {

mx.fastr/findbugs-exclude.xml

@@ -7,6 +7,10 @@
   <Match>
     <Class name="com.oracle.truffle.r.parser.RLexer"/>
   </Match>
+  <!-- exclude RAccuracyInfo (translated from GnuR) -->
+  <Match>
+    <Class name="com.oracle.truffle.r.runtime.RAccuracyInfo"/>
+  </Match>
   <!-- exclude generated node factory classes -->
   <Match>
       <Class name="~com\.oracle\.truffle\.r\.nodes\..*Factory(\$.*)?"/>