RFR: 8308041: [JVMCI] WB_IsGCSupportedByJVMCICompiler must enter correct JVMCI env

[Doug Simon]

The `WB_IsGCSupportedByJVMCICompiler` function in `whitebox.cpp` must use the same JVMCI environment (i.e. jarjvmci or libjvmci) that will be used by the `CompileBroker`. Otherwise, the question is being asked to the wrong JVMCI compiler implementation (which may not even exist in one of the 2 possible JVMCI environments).

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Commit messages:
 - WB_IsGCSupportedByJVMCICompiler must use JVMCI env used by the CompileBroker

Changes: https://git.openjdk.org/jdk/pull/13971/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13971&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8308041
  Stats: 2 lines in 1 file changed: 1 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/13971.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13971/head:pull/13971

PR: https://git.openjdk.org/jdk/pull/13971