[JVMCI] WB_IsGCSupportedByJVMCICompiler must enter correct JVMCI env

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).