RFR: JDK-8354316 : clang/linux build fails with -Wunused-result warning at XToolkit.c:695:9 [v2]

[Harshitha Onkar]

> The following line results in unused-result warning on linux/clang.
> 
> 
> /java.desktop/unix/native/libawt_xawt/xawt/XToolkit.c:695:9: error: ignoring return value of function
>  declared with 'warn_unused_result' attribute [-Werror,-Wunused-result]
>  695 | write ( AWT_WRITEPIPE, &wakeUp_char, 1 ); 
> 
> 
> There are two ways to handle it 
> 
> 1) Make changes to XToolkit.c such that the warning is no longer thrown. But throwing an error based on the result of `write ( AWT_WRITEPIPE, &wakeUp_char, 1 );` will result in unexpected behavioral changes and the best way to handle it is to have an empty if block with an appropriate comment.
> 
> 
> There was a discussion about the same line long ago and the reason the result of `write()` was not handled and it was left unchanged was not to introduce behavioral change - https://mail.openjdk.org/pipermail/awt-dev/2016-July/011626.html
> 
> 
> 2) Add unused-result to disabled warning section for clang similar to gcc - https://github.com/openjdk/jdk/blob/d1543429ff29ca0d761b8473b3fb8621abcd226d/make/modules/java.desktop/lib/AwtLibraries.gmk#L281. The 1st approach was picked over the 2nd since the usual recommendation is not to add to disabled warning section unless there is no other option.
> 
> NOTE: the fix has been tested on linux/gcc , it does need to be tested on linux/clang.

Harshitha Onkar has updated the pull request incrementally with one additional commit since the last revision:

  DTRACE added

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/25217/files
  - new: https://git.openjdk.org/jdk/pull/25217/files/f1172662..91f3d409

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=25217&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=25217&range=00-01

  Stats: 4 lines in 1 file changed: 0 ins; 3 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/25217.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25217/head:pull/25217

PR: https://git.openjdk.org/jdk/pull/25217