RFR(trivial): 8227512: [TESTBUG] Fix JTReg javac test failures with Graal

[Pengfei Li (Arm Technology China)]

Hi,

Please help review this small fix.
JBS: https://bugs.openjdk.java.net/browse/JDK-8227512
Webrev: http://cr.openjdk.java.net/~pli/rfr/8227512/

JTReg javac tests
* langtools/tools/javac/modules/InheritRuntimeEnvironmentTest.java
* langtools/tools/javac/file/LimitedImage.java
failed when Graal is used as JVMCI compiler.

These cases test javac behavior with the condition that observable modules are limited. But Graal is unable to be found in the limited module scope. This fixes these two tests by adding "jdk.internal.vm.compiler" into the limited modules.

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Thanks,
Pengfei