[foreign-jextract] RFR: 8259226: jextract should differentiate between clang errors vs other runtime issues [v2]

[Athijegannathan Sundararajan]

> Introducing ClangException for clang diagnostic errors and returning CLANG_ERROR for diagnostic errors. Also using OUTPUT_ERROR as intended.

Athijegannathan Sundararajan has updated the pull request incrementally with one additional commit since the last revision:

  Copyright year for new file should be 2021

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Changes:
  - all: https://git.openjdk.java.net/panama-foreign/pull/430/files
  - new: https://git.openjdk.java.net/panama-foreign/pull/430/files/8b765588..21f16307

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=panama-foreign&pr=430&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=panama-foreign&pr=430&range=00-01

  Stats: 3 lines in 3 files changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.java.net/panama-foreign/pull/430.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-foreign pull/430/head:pull/430

PR: https://git.openjdk.java.net/panama-foreign/pull/430