"CompileCommand" is used both as a enum type (compilerOracle.hpp), and a global variable (compiler_globals.hpp).

This makes very awkward to the enum type -- we are forced to use 'enum CompileCommand' in the source code whenever a type is needed:

This simple c++ file illustrates the problem:
================
enum class CompileCommand { a, b, c };
void foo(CompileCommand x) {}
char* CompileCommand; // can no longer use "CompileCommand" as a type
void good(enum CompileCommand x) {}
void bad(CompileCommand x) {}
==================
$ g++ -c ~/enum.cpp
/home/iklam/enum.cpp:5:6: error: variable or field ?bad? declared void
    5 | void bad(CompileCommand x) {}

Proposed fix:

The fix is to rename the enum type to CompileCommandEnum.

This also makes it possible to forward-declare the CompileCommandEnum without including compilerOracle.hpp. This improves HotSpot build time by reducing the number of .o files that includes compilerOracle.hpp from 456 to 16.