tests: list known failing tests

[marxin]

No description provided.

[Copilot]

Pull request overview

This PR updates the test ignores file to document known failing tests by adding issue references and new test exclusions.

• Adds 8 new SIMD test ignores for LLVM+loongarch64 architecture related to issue #6017
• Reformats multi-value test ignores section with proper issue reference #5943 and standardized formatting
• Adds new multi-value test ignores for llvm+loongarch64 and llvm+riscv64 platforms

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[Copilot]

The test paths use "::llvm::llvm" as the suffix, but all other similar test entries in this file use "::llvm::universal" as the suffix (see lines 43-58 for riscv64 and lines 69-84 for loongarch64). This inconsistency may indicate an error in the test path specification. Consider changing "::llvm::llvm" to "::llvm::universal" to match the established pattern.

Suggested change

	llvm+loongarch64 spec::simd::simd_f32x4::llvm::llvm
	llvm+loongarch64 spec::simd::simd_f64x2::llvm::llvm
	llvm+loongarch64 spec::simd::simd_load::llvm::llvm
	llvm+loongarch64 spec::simd::simd_splat::llvm::llvm
	llvm+loongarch64 spec::simd_f32x4::llvm::llvm
	llvm+loongarch64 spec::simd_f64x2::llvm::llvm
	llvm+loongarch64 spec::simd_load::llvm::llvm
	llvm+loongarch64 spec::simd_splat::llvm::llvm
	llvm+loongarch64 spec::simd::simd_f32x4::llvm::universal
	llvm+loongarch64 spec::simd::simd_f64x2::llvm::universal
	llvm+loongarch64 spec::simd::simd_load::llvm::universal
	llvm+loongarch64 spec::simd::simd_splat::llvm::universal
	llvm+loongarch64 spec::simd_f32x4::llvm::universal
	llvm+loongarch64 spec::simd_f64x2::llvm::universal
	llvm+loongarch64 spec::simd_load::llvm::universal
	llvm+loongarch64 spec::simd_splat::llvm::universal

[Copilot]

These test entries (lines 91-94) appear to duplicate the tests from lines 87-90, but with different path prefixes. Lines 87-90 use "spec::simd::simd_" while lines 91-94 use "spec::simd_". If these are indeed the same tests, the duplicates should be removed. If they represent different test paths, please verify that both path patterns are correct and necessary.

Suggested change

	llvm+loongarch64 spec::simd_f32x4::llvm::llvm
	llvm+loongarch64 spec::simd_f64x2::llvm::llvm
	llvm+loongarch64 spec::simd_load::llvm::llvm
	llvm+loongarch64 spec::simd_splat::llvm::llvm