RFR: 8341722: Fix some warnings as errors when building on Linux with toolchain clang

[Matthias Baesken]

On Tue, 8 Oct 2024 13:38:54 GMT, Matthias Baesken <mbaesken at openjdk.org> wrote:

> There are a few warnings as errors occurring when building on Linux with clang (clang15). Mostly these are some kind of 'unused' warnings.
> Might be related to https://bugs.openjdk.org/browse/JDK-8339156 .

I brought back `rslt`  but uncommented, as suggested.

Additionally I removed some special gcc warning setting; those disabled the symtab.c and LinuxDebuggerLocal.cpp  related warnings when compiling with gcc (brings clang and gcc behavior a bit closer together).

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PR Comment: https://git.openjdk.org/jdk/pull/21407#issuecomment-2402092775