Make constant expression evaluation FP-strict

https://docs.oracle.com/javase/specs/jls/se8/html/jls-15.html#jls-15.4

MOE_MIGRATED_REVID=139262607
diff --git a/java/com/google/turbine/binder/ConstEvaluator.java b/java/com/google/turbine/binder/ConstEvaluator.java
index 524cb5a..c94f01b 100644
--- a/java/com/google/turbine/binder/ConstEvaluator.java
+++ b/java/com/google/turbine/binder/ConstEvaluator.java
@@ -58,8 +58,12 @@
 import java.util.LinkedHashMap;
 import java.util.Map;
 
-/** Constant expression evaluation. */
-public class ConstEvaluator {
+/**
+ * Constant expression evaluation.
+ *
+ * <p>JLS §15.4 requires this class to be strictfp.
+ */
+public strictfp class ConstEvaluator {
 
   /** The symbol of the enclosing class. */
   private final ClassSymbol owner;