RFR: 8325163: Enable -Wpedantic on clang [v2]

[Julian Waters]

On Mon, 5 Feb 2024 10:58:17 GMT, Magnus Ihse Bursie <ihse at openjdk.org> wrote:

>> Inspired by (the later backed-out) [JDK-8296115](https://bugs.openjdk.org/browse/JDK-8296115), I propose to enable `-Wpedantic` for clang. This has already found some irregularities in the code, like mistakenly using `#import` instead of `#include`. In this patch, I disable warnings for these individual buggy or badly written files, but I intend to post follow-up issues on the respective teams to have them properly fixed.
>> 
>> Unfortunately, it is not possible to enable `-Wpedantic` on gcc, since individual warnings in `-Wpedantic` cannot be disabled. This means that code like this:
>> 
>> 
>> #define DEBUG_ONLY(code) code;
>> 
>> DEBUG_ONLY(foo());
>> 
>> 
>> will result in a `; ;`. This breaks the C standard, but is benign, and we use it all over the place. On clang, we can ignore this by `-Wno-extra-semi`, but this is not available on gcc.
>
> Magnus Ihse Bursie has updated the pull request incrementally with one additional commit since the last revision:
> 
>   FIx dtrace build

The following is all that I was able to find, on the latest gcc docs. Nothing came up for clang for the search term "-pedantic vs -Wpedantic"

> -pedantic-errors
> Give an error whenever the base standard (see -Wpedantic) requires a diagnostic, in some cases where there is undefined behavior at compile-time and in some other cases that do not prevent compilation of programs that are valid according to the standard. This is not equivalent to -Werror=pedantic: the latter option is unlikely to be useful, as it only makes errors of the diagnostics that are controlled by -Wpedantic, whereas this option also affects required diagnostics that are always enabled or controlled by options other than -Wpedantic.

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PR Comment: https://git.openjdk.org/jdk/pull/17687#issuecomment-1926946873