[llvm] [NFC][TableGen] Emit more readable builtin string table. (PR #105445)

[Rahul Joshi via llvm-commits]

jurahul wrote:

> ```c++
> Woverlength-strings
> ```

Actually, GCC docs suggest that this warning is not enabled for C++: https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html
That means that we can skip emitting these pragmas for this case as this is generated in a C++ file. This means adding an option to the emit function. I can roll that into this change as well.

https://github.com/llvm/llvm-project/pull/105445