Enable more C++ warnings?

[schuermans-roofline]

Hi IREE team!

I think the following flags that turn off C++ warnings can be removed with a few code changes (about 10 code locations):

-Wno-ambiguous-member-template
-Wno-char-subscripts
-Wno-gnu-alignof-expression
-Wno-gnu-variable-sized-type-not-at-end
-Wno-ignored-optimization-argument
-Wno-invalid-source-encoding
-Wno-mismatched-tags
-Wno-pointer-sign
-Wno-reserved-user-defined-literal
-Wno-return-type-c-linkage
-Wno-self-assign-overloaded
-Wno-sign-compare
-Wno-signed-unsigned-wchar
-Wno-strict-overflow
-Wno-trigraphs
-Wno-unknown-pragmas
-Wno-unknown-warning-option
-Wno-unused-command-line-argument
-Wno-unused-local-typedef
-Wno-user-defined-warnings
-Wno-missing-braces

So far, this has been tried using cmake on tag iree-3.8.0rc20250916 / hash e8050c352d on linux_x86_64 and with bazel on RooflineAI's fork on linux_x86_64, linux_riscv, linux_aarch8, and macosx_arm64.

Would you be interested in me opening a PR with the changes?

[maxbartel]

@benvanik I think you are the only active build system maintainer atm?