RFR: 8271186: Add UL option to replace newline char

[Yasumasa Suenaga]

Most of UL entries would print log in one line, however some categories (e.g. `exceptions`) have multiline entries as following:


[0.157s][info][exceptions] Exception <a 'java/lang/NullPointerException'{0x000000008b918f70}: test>
 thrown in interpreter method <{method} {0x00007f8335000248} 'main' '([Ljava/lang/String;)V' in 'Test'>
 at bci 9 for thread 0x00007f8330017160 (main)


It is ease to parse with log shipper (Fluent Bit, Logstash, and more) if UL can print all logs in one line.
Famous log shippers support multiline logs of course, but its configuration tends to be complex, and also some input plugins (e.g. TCP on Fluent Bit) do not support multiline logs.

So I want to introduce new UL option newline to replace `\n` to other chars. For example, the user specifies `newline=\\n` to UL output, newline char (`\n`) will replace `\\n`.

After this patch, we can get following logs with `newline=\\n`:


[0.166s][info][exceptions] Exception <a 'java/lang/NullPointerException'{0x000000008b918f70}: test>\n thrown in interpreter method <{method} {0x00007fbc81000248} 'main' '([Ljava/lang/String;)V' in 'Test'>\n at bci 9 for thread 0x00007fbc9c0171a0 (main)


I've also filed [CSR](https://bugs.openjdk.java.net/browse/JDK-8271188) for this issue, please review it.

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Commit messages:
 - add inclusion of os.hpp
 - 8271186: Add UL option to replace newline char

Changes: https://git.openjdk.java.net/jdk/pull/4885/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=4885&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8271186
  Stats: 82 lines in 4 files changed: 74 ins; 0 del; 8 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4885.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4885/head:pull/4885

PR: https://git.openjdk.java.net/jdk/pull/4885