Merge pull request #3833 from lucasallan/fixnum-bitlength

Fixnum#bit_length - uses bit inversion when the value is negative

core/src/main/java/org/jruby/RubyFixnum.java

@@ -1194,7 +1194,7 @@ public IRubyObject succ(ThreadContext context) {
     public IRubyObject bit_length(ThreadContext context) {
         long tmpValue = value;
         if (value < 0) {
-            tmpValue = Math.abs(value);
+            tmpValue = ~value;
         }
 
         return context.runtime.newFixnum(64 - Long.numberOfLeadingZeros(tmpValue));