RFR: 8376284: New test serviceability/sa/TestJhsdbJstackMixedCore.java from JDK-8374482 fails on Linux Alpine [v3]

[Yasumasa Suenaga]

> TestJhsdbJstackMixedCore.java introduced in [JDK-8374482](https://bugs.openjdk.org/browse/JDK-8374482) failed on Alpine because musl-c does not provide the symbol of signal trampoline (`__restore_rt` on Linux Kernel for AMD64) as following:
> 
> 
> java.lang.RuntimeException: '<signal handler called>' missing from stdout/stderr
> at jdk.test.lib.process.OutputAnalyzer.shouldContain(OutputAnalyzer.java:253)
> at TestJhsdbJstackMixedCore.runJstackMixed(TestJhsdbJstackMixedCore.java:62)
> at TestJhsdbJstackMixedCore.main(TestJhsdbJstackMixedCore.java:74)
> at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:104)
> at java.base/java.lang.reflect.Method.invoke(Method.java:565)
> at com.sun.javatest.regtest.agent.MainActionHelper$AgentVMRunnable.run(MainActionHelper.java:335)
> at java.base/java.lang.Thread.run(Thread.java:1516)
> 
> 
> It would success if debuginfo is installed, but it should be skipped if the symbol is not available.
> See JBS for details.

Yasumasa Suenaga has updated the pull request incrementally with one additional commit since the last revision:

  Clarify comments regarding debuginfo retrieval

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/29480/files
  - new: https://git.openjdk.org/jdk/pull/29480/files/77d07827..1913d6bb

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=29480&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=29480&range=01-02

  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/29480.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29480/head:pull/29480

PR: https://git.openjdk.org/jdk/pull/29480