Fix assorted ErrorProne warnings.

RELNOTES: None.
PiperOrigin-RevId: 167574104
diff --git a/src/main/java/com/google/devtools/build/lib/buildtool/ExecutionTool.java b/src/main/java/com/google/devtools/build/lib/buildtool/ExecutionTool.java
index cf6c4e2..83d259c 100644
--- a/src/main/java/com/google/devtools/build/lib/buildtool/ExecutionTool.java
+++ b/src/main/java/com/google/devtools/build/lib/buildtool/ExecutionTool.java
@@ -96,7 +96,9 @@
 import com.google.devtools.build.lib.vfs.PathFragment;
 import java.io.IOException;
 import java.io.OutputStream;
+import java.io.OutputStreamWriter;
 import java.io.PrintWriter;
+import java.nio.charset.StandardCharsets;
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.HashMap;
@@ -606,7 +608,7 @@
     private final PrintWriter log;
 
     private ExplanationHandler(OutputStream log, String optionsDescription) {
-      this.log = new PrintWriter(log);
+      this.log = new PrintWriter(new OutputStreamWriter(log, StandardCharsets.UTF_8));
       this.log.println("Build options: " + optionsDescription);
     }