RFR: 8273804: Platform.isTieredSupported should handle the no-compiler case

[Aleksey Shipilev]

Happens with Zero tests:


$ CONF=linux-x86_64-zero-fastdebug make exploded-test TEST=compiler/codecache/CheckSegmentedCodeCache.java
...

java.lang.NullPointerException: Cannot invoke "String.contains(java.lang.CharSequence)" because "jdk.test.lib.Platform.compiler" is null
at jdk.test.lib.Platform.isTieredSupported(Platform.java:82)
at compiler.codecache.CheckSegmentedCodeCache.verifySegmentedCodeCache(CheckSegmentedCodeCache.java:61)
at compiler.codecache.CheckSegmentedCodeCache.main(CheckSegmentedCodeCache.java:108)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:568)
at com.sun.javatest.regtest.agent.MainWrapper$MainThread.run(MainWrapper.java:127)
at java.base/java.lang.Thread.run(Thread.java:833) 


Additional testing:
 - [x] Linux x86_64 Zero, `compiler/codecache/CheckSegmentedCodeCache.java` now properly fails with "no compilers" error

-------------

Commit messages:
 - Fix

Changes: https://git.openjdk.java.net/jdk/pull/5528/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=5528&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8273804
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5528.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5528/head:pull/5528

PR: https://git.openjdk.java.net/jdk/pull/5528