RFR: 8325163: Enable -Wpedantic on clang

[Kim Barrett]

On Fri, 2 Feb 2024 15:22:03 GMT, Magnus Ihse Bursie <ihse at openjdk.org> wrote:

> #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.

All of the -Wpedantic warnings for extra ';' in C++ code I looked at look to
me like a gcc bug (or bugs). C++11 added "empty-declaration", which is
permitted anywhere a normal declaration is permitted (C++14 7), as well as for
class member declarations (C++14 9.2).

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96068
seems to have fixed some, but not all, cases.  It looks like it only removed
the warnings for empty declarations at namespace scope.  I couldn't find
anything for other cases, including empty class member declarations.

I consider the "format '%p' expects argument of type 'void*" warnings to be
not at all helpful.  Fortunately we don't use '%p' in HotSpot, but I don't
know how other groups might feel having this inflicted on them.

Because of the vast numbers of those, I ran out of patience trying to find and
examine other warnings triggered by this option.

Based on that, I'm not feeling very keen on this change, at least not for a future
version applying to gcc builds.

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PR Comment: https://git.openjdk.org/jdk/pull/17687#issuecomment-1926154325