Fix RISC-V Test Failures in ./x test for Multiple Codegen and Assembly Cases

[CaiWeiran]

This PR addresses and resolves several test failures that occurred when running ./x test on the RISC-V architecture. The issues were due to platform-specific behavior, ABI differences, or code generation inconsistencies specific to RISC-V.

The following tests have been fixed:

• assembly/dwarf-mixed-versions-lto.rs
• codegen/const-vector.rs
• codegen/enum/enum-aggregate.rs
• codegen/simd/extract-insert-dyn.rs
• codegen/transmute-scalar.rs
• codegen/uninhabited-transparent-return-abi.rs

All changes have been tested locally with ./x test on a RISC-V target and now pass as expected.

Notes:

• These fixes are scoped specifically to enable full test suite compliance for RISC-V targets.
• No changes were made that affect other architectures.

[rustbot]

r? @Mark-Simulacrum

rustbot has assigned @Mark-Simulacrum.
They will have a look at your PR within the next two weeks and either review your PR or reassign to another reviewer.

Use r? to explicitly pick a reviewer

[bors]

☔ The latest upstream changes (presumably #143502) made this pull request unmergeable. Please resolve the merge conflicts.