RFR: JDK-8300080: offset_of for GCC/Clang exhibits undefined behavior and is not always a compile-time constant

[Justin King]

The implementation of `offset_of` for GCC/Clang only deals with types are aligned to 16 bytes or less, if they are more, such as `zCollectedHeap` the behavior is undefined. UBSan also suggests that `offset_of` is not always a compile time constant, as the stack trace came from the dynamic loader during library loading. This patch changes `offset_of` to use `offsetof` and disables the warning `invalid-offsetof` for the JVM.

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Commit messages:
 - offset_of for GCC/Clang exhibits undefined behavior and is not always a compile-time constant

Changes: https://git.openjdk.org/jdk/pull/11978/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=11978&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8300080
  Stats: 19 lines in 2 files changed: 1 ins; 15 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/11978.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11978/head:pull/11978

PR: https://git.openjdk.org/jdk/pull/11978