RFR: 8297967: Make frame::safe_for_sender safer [v4]

[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:

  More SafeFetch

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/11461/files
  - new: https://git.openjdk.org/jdk/pull/11461/files/f7762551..32cced6e

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=11461&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=11461&range=02-03

  Stats: 24 lines in 4 files changed: 24 ins; 0 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