[release/6.0] Fix gcc warnings during mono linux-x64 build (backport of #60675)

[ayakael]

Backport of #60675 to release/6.0

Per @am11

main with Debug configuration: 822 warnings - http://sprunge.us/2GzrDE
PR with Debug configuration: 3 warnings related to deprecated sys/sysctl.h includes - http://sprunge.us/JuyA3K

after fixing Debug warnings, there were 13 additional warnings in Release configuration:
http://sprunge.us/PJCivP

PR with Release configuration: (same) 3 warnings - http://sprunge.us/NwKHNE

Used:

same docker image used in CI for coreclr gcc build: mcr.microsoft.com/dotnet-buildtools/prereqs:debian-11-gcc11-amd64-20210916125744-f42d766
build command: runtime/build.sh mono -gcc -c Debug (and later with -c Release)

Customer impact

Mono flavored-runtime will be less prone to errors

Testing

• unit tests in ci
• source-build build within Alpine environment passes

Risk

Low, as it is already in main, and only activates when cmake for linux test passes.

[ayakael]

@am11 Is this something that looks good for you as far as a direct backport, or is there something missing on my implementation?

[vargaz]

Why do these warning fixes need to be backported ?

[ayakael]

Without this, build of dotnet6 on s390x has issues. This was first backported to Fedora's package, which Alpine Linux has then applied to our package in getting that up to speed. @omajid can fill in on the details.

[omajid]

The commit doesn't spell it out, but this also fixes build errors when building .NET with clang 15. We needed this to be able to build .NET 6 on Fedora 37.

[am11]

This a partial backport of the linked PR. Looks good. Thanks!

The commit doesn't spell it out, but this also fixes build errors when building .NET with clang 15.

Understandable; 577a70a is a one year old commit, while clang-15 was released two months ago.

[carlossanlop]

@vargaz @lambdageek @marek-safar this needs to go through Tactics. When/if this is ready, please add the servicing-consider label and send an email to Tactics requesting merge approval.

[carlossanlop]

Ping @lambdageek @marek-safar @vargaz. Also, the CI seems to be stuck, so it needs a restart. I'm closing and reopening.

[carlossanlop]

@vargaz @lambdageek @marek-safar this has not been approved by Tactics yet. Can you please send the approval email? The deadline is the 14th.

[lambdageek]

@vargaz @marek-safar @carlossanlop I emailed tactics

[vargaz]

Approved by tactics.

[carlossanlop]

Signed off by area owner.
Approved by Tactics.
CI green.
No OOB package authoring changes needed for this.
Ready to merge.