Fix issues flagged by compiling clr.aot with clang on Windows

[MichalStrehovsky]

Out of curiosity I let copilot build clr.aot with clang. Most are signed/unsigned comparison mismatches that we treat as errors on Windows (/we4018) and copilot matched it with -Wsign-compare.

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[Copilot]

Pull request overview

This PR adjusts several native/runtime sources to compile cleanly under clang on Windows by addressing common warning patterns (signed/unsigned loop indices, format-string type mismatches, unreachable control-flow annotations, and header include casing).

Changes:

• Switch loop indices to size_t where the bound is sizeof/ARRAY_SIZE-derived.
• Adjust GUID formatting to better match snprintf’s %x expectations.
• Minor portability/diagnostic fixes: add missing standard include, add UNREACHABLE(), fix header include casing, and mark a destructor virtual.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/native/minipal/xoshiro128pp.c	Add <stddef.h> and use size_t loop index to avoid signed/unsigned comparisons.
src/native/minipal/guid.c	Cast GUID components for snprintf formatting (but see review comment about completing the casts).
src/coreclr/utilcode/stacktrace.cpp	Use size_t for an ARRAY_SIZE-bounded loop.
src/coreclr/utilcode/pedecoder.cpp	Cast rcName to satisfy strlen’s parameter type in this context.
src/coreclr/utilcode/debug.cpp	Add UNREACHABLE() after RaiseFailFastException to satisfy noreturn analysis.
src/coreclr/nativeaot/Runtime/windows/PalMinWin.cpp	Remove redundant _T definition and fix include casing for NativeContext.h.
src/coreclr/nativeaot/Runtime/windows/CoffNativeCodeManager.h	Mark destructor virtual to address polymorphic-type destructor diagnostics.
src/coreclr/jit/utils.cpp	Fix signed/unsigned comparison by casting strBufferSize before comparing with bufferSize.

Comments suppressed due to low confidence (1)

src/native/minipal/guid.c:76

• The snprintf format string uses %x/%02x/%04x (expects unsigned int after default promotions), but only Data1 is cast. The remaining arguments (Data2, Data3, and Data4[i]) may still be passed as int due to default promotions, which is undefined behavior and can still trigger clang -Wformat diagnostics. Casting all arguments (or switching to <inttypes.h> macros) avoids both UB and remaining warnings.

    int32_t nBytes = snprintf(guidString, len, "{%08x-%04x-%04x-%02x%02x-%02x%02x%02x%02x%02x%02x}",
        (unsigned int)guid.Data1, guid.Data2, guid.Data3,
        guid.Data4[0], guid.Data4[1],
        guid.Data4[2], guid.Data4[3],
        guid.Data4[4], guid.Data4[5],
        guid.Data4[6], guid.Data4[7]);

[MichalStrehovsky]

/ba-g widespread wasm infra issue that doesn't produce usable output