Fixes version parsing for WARNING situations

(cherry picked from commit ff3824b)

build.java

@@ -1,6 +1,3 @@
-import static java.nio.charset.StandardCharsets.UTF_8;
-import static java.nio.file.StandardCopyOption.REPLACE_EXISTING;
-
 import java.io.File;
 import java.io.IOException;
 import java.io.InputStream;
@@ -43,6 +40,9 @@
 import java.util.stream.IntStream;
 import java.util.stream.Stream;
 
+import static java.nio.charset.StandardCharsets.UTF_8;
+import static java.nio.file.StandardCopyOption.REPLACE_EXISTING;
+
 public class build
 {
     static final Logger logger = LogManager.getLogger(build.class);
@@ -337,8 +337,21 @@ else if (archiveName.endsWith("zip") && !IS_WINDOWS)
 
     private static String getMandrelVersion(FileSystem fs, OperatingSystem os, Path mandrelRepo)
     {
-        String mandrelVersion = os.exec(Mx.mandrelVersion(fs.mxHome(), fs.mandrelRepo()), true).get(0);
-
+        final Pattern startsWithNumber = Pattern.compile("^\\d.*");
+        String mandrelVersion = null;
+        final List<String> o = os.exec(Mx.mandrelVersion(fs.mxHome(), fs.mandrelRepo()), true);
+        for (String s : o)
+        {
+            logger.info("mx's graalvm-version output: " + s);
+            if (mandrelVersion == null && startsWithNumber.matcher(s).matches())
+            {
+                mandrelVersion = s;
+            }
+        }
+        if (mandrelVersion == null)
+        {
+            throw new RuntimeException("Could not determine Mandrel version from mx graalvm-version output");
+        }
         if (mandrelVersion.endsWith("-dev"))
         {
             final Tasks.Exec command = Tasks.Exec.of(Arrays.asList("git", "rev-parse", "--short", "HEAD"), mandrelRepo);