[llvm] [Mips] Track ISA mode and distinguish ELF data labels (PR #228883)

[Jiaxun Yang via llvm-commits]

FlyGoat wrote:

Merge dependency: https://github.com/llvm/llvm-project/pull/228882 must land first so MIPS16 symbol marking can preserve `STO_MIPS_MIPS16` (0xf0) without an assertion or loss of bit 4. This PR contains only the ISA-mode commit.

https://github.com/llvm/llvm-project/pull/228883