backport(8.0): Fix runtime architecture detection logic in ANCM

[DeagleGross]

Description

Backport of #63652 to net8.0

A change (#61894) improved algorithm to determine the architecture of a binary by switching away from GetBinaryTypeW (which seems to load the exe into executable space which might trigger custom windows policies). It was backported to net8.0: #62037.

However, we spotted that sometimes function incorrectly chooses a binary of an incompatible architecture, resulting in crashing site load.

Current change specifically checks for a full compatibility of bitness and architecture.

Fixes #63650

Customer Impact

For example users hosting x86 app on x64 machine / x64 app on arm64 machine are impacted unless current change is merged and used.

Regression?

• Yes
• No

Risk

• High
• Medium
• Low

Impacts users who are using different process architecture then what where.exe outputs trying to find dotnet binary. It takes OS / process / dotnet arch installed combination to affect the behavior.

Verification

• Manual (required)
• Automated

Packaging changes reviewed?

• Yes
• No
• N/A

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[Copilot]

Pull Request Overview

This PR backports a fix for runtime architecture detection logic in the ASP.NET Core Module (ANCM) to the .NET 8.0 branch. The changes replace a simple x86/x64 bitness check with comprehensive processor architecture detection that supports x86, AMD64, and ARM64 architectures.

Key changes:

• Introduces a new ProcessorArchitecture enum with proper architecture detection
• Replaces binary bitness checking with PE header machine type analysis
• Updates dotnet.exe selection logic to match process architecture instead of just bitness

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
ProcessorArchitecture.h	New header defining processor architecture enum and string conversion utility
HostFxrResolver.h	Updates method signature from IsX64 to GetFileProcessorArchitecture and adds include
HostFxrResolver.cpp	Replaces bitness detection with comprehensive architecture matching using PE header analysis
Environment.h	Adds new method declaration for getting current process architecture
Environment.cpp	Implements compile-time architecture detection for current process

[danmoseley]

@DeagleGross feel free to send the usual mail to tactics for the backport approval.

Note -- there is some precedent for holding off on backports until they've had some bake time in main. Or even, take the 9.0 backport but delay the 8.0 backport a month or two. It's really a risk decision. Your judgement.