Add R2R knob to force value of TargetAllowsRuntimeCodeGeneration

[BrzVlad]

iOS like configuration can be obtained by passing --target-allows-runtime-code-generation:false.

When runtime is built with dynamiccodecompiled false, this also makes sure that corelib is build in this configuration, just to make sure that corerun and testhost respect it. We don't yet test this configuration on CI, so no additional changes are done yet on the testing infra.

dotnet/performance job expected crossgen2 built from runtime with dynamiccodecompiled to have TargetAllowsRuntimeCodeGeneration automatically disabled. This regressed following the removal of the FEATURE_DYNAMIC_CODE_COMPILED hack in https://github.com/dotnet/runtime/pull/130622/changes.

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[Copilot]

Pull request overview

This PR adds an explicit crossgen2 command-line knob to override the inferred TargetAllowsRuntimeCodeGeneration value, and wires it into the CoreCLR corelib crossgen invocation so that builds with FeatureDynamicCodeCompiled=false produce matching ReadyToRun behavior.

Changes:

• Add --target-allows-runtime-code-generation option to crossgen2 (nullable bool override).
• Use the override (when provided) instead of the target OS/arch heuristic in crossgen2 compilation setup.
• Pass the knob from crossgen-corelib.proj based on $(FeatureDynamicCodeCompiled) so corelib R2R generation matches the runtime configuration.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
src/coreclr/tools/aot/crossgen2/Properties/Resources.resx	Adds the help/description string for the new CLI option.
src/coreclr/tools/aot/crossgen2/Program.cs	Applies the option override and feeds it into ReadyToRun compilation behavior and context construction.
src/coreclr/tools/aot/crossgen2/Crossgen2RootCommand.cs	Declares and registers the new --target-allows-runtime-code-generation option.
src/coreclr/crossgen-corelib.proj	Propagates $(FeatureDynamicCodeCompiled) into crossgen2 via the new option.

[Copilot]

🔵 Needs a closer look

Review details

Suppressed comments (1)

Previously missed (1) — in code that hasn't changed since the last review.

src/coreclr/crossgen-corelib.proj:164

• $(FeatureDynamicCodeCompiled) is treated as boolean-like across the build (e.g., anything other than "true" is effectively false), but this command line forwards the raw value to a bool option. If the property is ever set to a non-"true" token like 0, crossgen2 argument parsing is likely to fail. Consider normalizing/mapping the property to an explicit true/false token before passing it.

      <CrossGenDllCmd Condition="'$(FeatureDynamicCodeCompiled)' != ''">$(CrossGenDllCmd) --target-allows-runtime-code-generation:$(FeatureDynamicCodeCompiled)</CrossGenDllCmd>

• Files reviewed: 4/4 changed files
• Comments generated: 0 new
• Review effort level: Lite