[jdk11u-dev] RFR: 8313796: AsyncGetCallTrace crash on unreadable interpreter method pointer

[Ben Taylor]

Backport [8313796](https://bugs.openjdk.org/browse/JDK-8313796) to resolve a hotspot crash. Passes jtreg tier 1-4 tests.

This change required the following modifications:
- Remove riscv code, as the riscv port is not present in jdk 11
- Replace `nullptr` with `NULL` to accommodate older C++ standards/compilers

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Commit messages:
 - 8313796: AsyncGetCallTrace crash on unreadable interpreter method pointer

Changes: https://git.openjdk.org/jdk11u-dev/pull/2079/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk11u-dev&pr=2079&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8313796
  Stats: 15 lines in 6 files changed: 11 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk11u-dev/pull/2079.diff
  Fetch: git fetch https://git.openjdk.org/jdk11u-dev.git pull/2079/head:pull/2079

PR: https://git.openjdk.org/jdk11u-dev/pull/2079