RFR(S) : 8147017 : Platform.isGraal should be removed

[Igor Ignatyev]

http://cr.openjdk.java.net/~iignatyev//8147017/webrev.00/index.html
> 16 lines changed: 2 ins; 8 del; 6 mod; 

Hi all,

jdk.test.lib.Platform.isGraal method assumes that JVM w/ Graal as JIT has 'Graal VM' in its name, which is wrong, and caused other to incorrectly assume that '-graal' flag exist and must be used to select Graal compiler. the patch removes this method and updates its only meaningful usage in TestGCLogMessages test. TestGCLogMessages test should use LogMessageWithLevelC2OrJVMCIOnly only when c2 or graal is available, so it's been updated to use corresponding methods of sun.hotspot.code.Compiler class, which requires WhiteBoxAPI being enabled. 


JBS: https://bugs.openjdk.java.net/browse/JDK-8147017
webrev: http://cr.openjdk.java.net/~iignatyev//8147017/webrev.00/index.html
testing: tier1 + TestGCLogMessages w/ different JIT configurations

Thanks,
-- Igor