RFR: JDK-8296995: ostream should handle snprintf(3) errors in release builds [v5]

[Thomas Stuefe]

> Small fix for a very unlikely problem. 
> 
> All streams in ostream.hpp end up using `os::snprintf()`, which uses `::vsnprintf()`. `vsnprintf(3)`can fail and return -1. 
> 
> The chance for this to happen is small. snprintf errors are usually encoding errors though not always (see third example at https://stackoverflow.com/questions/65334245/what-is-an-encoding-error-for-sprintf-that-should-return-1). I found "%ls" in one place in windows coding, so I am not sure we can always exclude the possibility of wide strings being used in our code base, or that of printing with outside-provided format strings.
> 
> In case of an error, we assert in debug builds but don't handle it in release. There, this situation gets misdiagnosed later as a buffer overflow because we cast the signedness of the result away (see `outputStream::do_vsnprintf()`). 
> 
> ---
> 
> The patch is trivial. The most exciting thing is the gtest, I guess.
> 
> In release builds, we now treat this condition as an empty string write. I considered printing a clear marker into the stream instead, e.g. "ENCODING ERROR", but ultimately did not do it.

Thomas Stuefe has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains five additional commits since the last revision:

 - copyrights
 - erge branch 'master' into JDK-8296995-ostream-handle-sprintf-errors
 - fix copyright
 - feedback martin
 - JDK-8296995-ostream-handle-sprintf-errors

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Changes:
  - all: https://git.openjdk.org/jdk/pull/11160/files
  - new: https://git.openjdk.org/jdk/pull/11160/files/b41f13d4..407345ca

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=11160&range=04
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=11160&range=03-04

  Stats: 384575 lines in 5749 files changed: 193196 ins; 138159 del; 53220 mod
  Patch: https://git.openjdk.org/jdk/pull/11160.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11160/head:pull/11160

PR: https://git.openjdk.org/jdk/pull/11160