[llvm] [StrTable] Use string literal emission for intrinsics on non-MSVC platforms (PR #124856)

[Reid Kleckner via llvm-commits]

rnk wrote:

> Not sure I understood the point of moving the option from one cpp file to another. It is still `extern` in the other file, **Sequence**ToOffsetTable.h, and could also be extern in **String**ToOffsetTable.h(?)

The other cpp file is in the `llvm-tblgen` binary, not the TableGen library used by other subproject tablegen binaries (`clang-tblgen` and `mlir-tblgen`), so referencing it this way would cause link errors. It needs to live in some lib/TableGen cpp file, so I made one rather than shoehorning it into an existing cpp file.

https://github.com/llvm/llvm-project/pull/124856