RFR: Fix Minimal VM build failures [v4]

[Aleksey Shipilev]

> Minimal VM configs have no C2 and no JVMTI. New Loom code fails the Minimal VM builds because of this. See for example GHA runs: https://github.com/shipilev/loom/runs/3717293969?check_suite_focus=true
> 
> C2 needs just a little bit of protection when reaching to `DerivedPointersTable`.
> 
> JVMTI needs a bit more work. `jvmtiExport` and `jvmtiThreadState` headers are usually included even with JVMTI turned off, but `.cpp` would not be compiled without JVMTI. Therefore, non-trivial implementations should go into `.cpp`. Plus, some of the paths that call the actual methods declared but not implemented without JVMTI should be protected with `INCLUDE_JVMTI`.
> 
> Additional testing:
>  - [x] Linux x86_64 server, `tier1_loom` still passes (includes JVMTI tests)
>  - [x] Linux x86_64 minimal now builds, runs `tier1_loom` (cannot pass JVMTI tests without JVMTI)

Aleksey Shipilev has updated the pull request incrementally with one additional commit since the last revision:

  Remove excessive guard

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

Changes:
  - all: https://git.openjdk.java.net/loom/pull/67/files
  - new: https://git.openjdk.java.net/loom/pull/67/files/9ba55eda..c78adb04

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=loom&pr=67&range=03
 - incr: https://webrevs.openjdk.java.net/?repo=loom&pr=67&range=02-03

  Stats: 2 lines in 1 file changed: 0 ins; 2 del; 0 mod
  Patch: https://git.openjdk.java.net/loom/pull/67.diff
  Fetch: git fetch https://git.openjdk.java.net/loom pull/67/head:pull/67

PR: https://git.openjdk.java.net/loom/pull/67