JIT: Remove overzealous fake-splitting assert for x86 unwind info

[amanasifkhalid]

This assert was hit by Antigen recently. If we are doing fake hot/cold splitting, the JIT should tell the VM to reserve just one unwind info for the main function entry, regardless of whether it is split. However, we still need to reserve unwind infos for the funclets. Thus, this assert doesn't make sense.

[Copilot]

Pull Request Overview

This PR removes an overzealous debug-only assertion related to fake procedure splitting in the JIT's x86 unwind info handling. The change ensures that when fake-splitting is enabled, the JIT no longer asserts on non-root funclets, and in release builds the unwind reservation proceeds consistently.

• Remove assert in debug mode when fake procedure splitting is enabled.
• Add a comment clarifying that all unwind info is treated as hot during fake-splitting.
• Adjust the control flow to conditionally call unwindReserveFuncHelper based on the fake-splitting configuration.

Comments suppressed due to low confidence (1)

src/coreclr/jit/unwindx86.cpp:123

• Consider adding a brief comment explaining that in release builds the unwindReserveFuncHelper call always executes, while in debug builds it is skipped when fake procedure splitting is enabled. This clarification can help future maintainers understand the conditional behavior.

        INDEBUG(if (!JitConfig.JitFakeProcedureSplitting()))

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[amanasifkhalid]

@dotnet/jit-contrib PTAL, thanks!

[amanasifkhalid]

ping @dotnet/jit-contrib