RFR: 8297967: Make frame::safe_for_sender safer [v5]

[Johannes Bechberger]

> Makes frame::safe_for_sender safer by using os::is_readable_pointer to check the location of the return address.

Johannes Bechberger has updated the pull request incrementally with one additional commit since the last revision:

  Remove check for value that might be null

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Changes:
  - all: https://git.openjdk.org/jdk/pull/11461/files
  - new: https://git.openjdk.org/jdk/pull/11461/files/32cced6e..971553fc

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=11461&range=04
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=11461&range=03-04

  Stats: 4 lines in 4 files changed: 0 ins; 4 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/11461.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11461/head:pull/11461

PR: https://git.openjdk.org/jdk/pull/11461