RFR: JDK-8308288: Fix xlc17 clang warnings in shared code [v2]

[JoKern65]

On Fri, 26 May 2023 08:31:46 GMT, JoKern65 <duke at openjdk.org> wrote:

>> When using the new xlc17 compiler (based on a recent clang) to build OpenJDk on AIX , we run into various "warnings as errors".
>> Some of those are in shared codebase and could be addressed by small adjustments.
>> A lot of those changes are in hotspot, some might be somewhere else in the OpenJDK C/C++ code.
>
> JoKern65 has updated the pull request incrementally with one additional commit since the last revision:
> 
>   forgotton _

Here are the reasons for the disabled warnings in make/modules/java.base/Lib.gmk
   DISABLED_WARNINGS_clang_aix_DefaultProxySelector.c := deprecated-non-prototype, \
    DISABLED_WARNINGS_clang_aix_NetworkInterface.c := gnu-pointer-arith, \
    DISABLED_WARNINGS_clang_aix_UnixNativeDispatcher.c := undef, \

src/java.base/unix/native/libnet/DefaultProxySelector.c:378:41:22: error: passing arguments to a function without a prototype is deprecated in all versions of C and is not supported in C2x [-Werror,-Wdeprecated-non-prototype]
    proxies = (*g_proxy_resolver_lookup)(resolver, uri, NULL, &error);
                                                             ^

src/java.base/unix/native/libnet/NetworkInterface.c:1612:24: error: arithmetic on a pointer to void is a GNU extension [-Werror,-Wgnu-pointer-arith]
    end = (void *)nddp + size;
     ~~~~~~~~~~~~ ^

src/java.base/unix/native/libnio/fs/UnixNativeDispatcher.c:1251:7: error: '_ALLBSD_SOURCE' is not defined, evaluates to 0 [-Werror,-Wundef]
#elif _ALLBSD_SOURCE
      ^

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PR Comment: https://git.openjdk.org/jdk/pull/14146#issuecomment-1564143664