8343190: GHA: Try building JTReg several times

Reviewed-by: erikj, ihse

.github/actions/build-jtreg/action.yml

@@ -52,8 +52,24 @@ runs:
 
     - name: 'Build JTReg'
       run: |
-        # Build JTReg and move files to the proper locations
-        bash make/build.sh --jdk "$JAVA_HOME_17_X64"
+        # Try building JTReg several times, backing off exponentially on failure.
+        # ~500 seconds in total should be enough to capture most of the transient
+        # failures.
+        for I in `seq 0 8`; do
+          rm -rf build/images/jtreg
+          bash make/build.sh --jdk "$JAVA_HOME_17_X64" && break
+          S=$(( 2 ** $I ))
+          echo "Failure. Waiting $S seconds before retrying"
+          sleep $S
+        done
+
+        # Check if build was successful
+        if [ ! -d build/images/jtreg ]; then
+          echo "Build failed"
+          exit 1;
+        fi
+
+        # Move files to the proper locations
         mkdir ../installed
         mv build/images/jtreg/* ../installed
       working-directory: jtreg/src