RFR: 8312591: GCC 6 build failure after JDK-8280982 [v2]

[Jie Fu]

On Thu, 27 Jul 2023 19:01:35 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> There is a simple build failure after [JDK-8280982](https://bugs.openjdk.org/browse/JDK-8280982) with older GCCs:
>> 
>> 
>> * For target support_native_java.desktop_libawt_xawt_screencast_pipewire.o:
>> In file included from /home/buildbot/worker/build-jdkX-debian9/build/src/java.desktop/unix/native/libpipewire/include/spa/buffer/buffer.h:12:0,
>>                  from /home/buildbot/worker/build-jdkX-debian9/build/src/java.desktop/unix/native/libpipewire/include/pipewire/stream.h:171,
>>                  from /home/buildbot/worker/build-jdkX-debian9/build/src/java.desktop/unix/native/libawt_xawt/awt/screencast_pipewire.h:36,
>>                  from /home/buildbot/worker/build-jdkX-debian9/build/src/java.desktop/unix/native/libawt_xawt/awt/screencast_pipewire.c:33:
>> /home/buildbot/worker/build-jdkX-debian9/build/src/java.desktop/unix/native/libpipewire/include/spa/utils/defs.h:61:24: error: "__clang_major__" is not defined [-Werror=undef]
>>  #elif __GNUC__ >= 7 || __clang_major__ >= 10
>>                         ^~~~~~~~~~~~~~~
>> 
>> 
>> There is an obvious fix for this: we need to check for `defined(__GNUC__)` explicitly before touching `__clang_major__`.
>> 
>> (Yes, GCC 6 is old; but we would like to make sure it builds until we run into hard to resolve build issues. This allows modern JDKs to be built in legacy enterprise environments for e.g. portable builds.)
>> 
>> Additional testing:
>>  - [x] Linux GCC 6 fastdebug build (passes with HarfBuzz warnings, to be fixed separately)
>
> Aleksey Shipilev has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Disable the warnings instead

It seems better not touching the 3rd party source code.

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Marked as reviewed by jiefu (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/14995#pullrequestreview-1551001231