RFR: 8261098: Add clhsdb "findsym" command [v3]

[Chris Plummer]

> Add "findsym" to clhsdb. See the CR and CSR for details. The [CSR](https://bugs.openjdk.java.net/browse/JDK-8261101) still needs a reviewer.
> 
> There is a fix in LinuxDebuggerLocal_lookupByName0() to allow passing in NULL for the dso name. This is allowed, and in fact even not null it gets ignored. It is needed by the new findsym support in order for the following to work, which passes in null for the dso name:
> 
> `    Address addr = VM.getVM().getDebugger().lookup(null, symbol);`
> 
> There is one other somewhat unrelated fix in the test:
> 
>  -            String value = parts[1];
>  +           String value = parts[1].split(linesep)[0];
> 
> This is suppose to capture just the value at the specified address, but it also captures the newline and some text after. The result if that when `findpc <value>` is executed, it also executes another command or two of garbage commands after that, which produce errors. They were not impacting the test, but were noticeable in the log. I first noticed it when similar code in the new part of the test had the same issue.

Chris Plummer has updated the pull request incrementally with one additional commit since the last revision:

  Improve handling of NULL objectName

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/2567/files
  - new: https://git.openjdk.java.net/jdk/pull/2567/files/ba3464c4..1a772c3d

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=2567&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=2567&range=01-02

  Stats: 5 lines in 2 files changed: 0 ins; 0 del; 5 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2567.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2567/head:pull/2567

PR: https://git.openjdk.java.net/jdk/pull/2567