[jdk17u-dev] RFR: 8372439: build-test-lib is broken

[Min Choi]

`make build-test-lib` is broken. 

https://github.com/openjdk/jdk17u-dev/pull/3917 was not tested by the "make build-test-lib", and introduced a bug
https://github.com/openjdk/jdk17u-dev/pull/1801 added incorrect "-add-exports" and was tested by the  "make build-test-lib", but it did not have the patch above.

`classfile` does not exist in JDK17

Ran `make build-test-lib` locally, all builds pass.

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Commit messages:
 - Fix 'make build-test-lib' and get rid of unnecessary classfile exports that only exist in JDK21+

Changes: https://git.openjdk.org/jdk17u-dev/pull/4195/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk17u-dev&pr=4195&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8372439
  Stats: 6 lines in 1 file changed: 2 ins; 4 del; 0 mod
  Patch: https://git.openjdk.org/jdk17u-dev/pull/4195.diff
  Fetch: git fetch https://git.openjdk.org/jdk17u-dev.git pull/4195/head:pull/4195

PR: https://git.openjdk.org/jdk17u-dev/pull/4195