RFR (T/XXS) 8222747: [Graal] mx_subprocess files miss testing VM flags

[Ekaterina Pavlova]

Hi,

Please review small change which fixes command line written in 'mx_subprocess.cmd' file used by some Graal unit tests.


     JBS: https://bugs.openjdk.java.net/browse/JDK-8222747
  webrev: http://cr.openjdk.java.net/~epavlova//8222747/webrev.00/index.html
testing: run graalunit tests in all testing configurations


Thanks,
-katya