[lld] [lld][ELF] Introduce an option to keep data section prefix. (PR #148985)

[Fangrui Song via llvm-commits]

MaskRay wrote:

> This change implements section grouping for {.data.rel.ro, .data, .rodata, .bss} to group .hot input sections to .<section>.hot in the output and to group .unlikely input sections to .<section>.unlikely. The grouping functionality is gated under new lld option -z,keep-data-section-prefix.

The description should be updated to describe the .rodata.cstN.hot special case. Ideally just list the literal mapping rules

```
.data.rel.ro.hot.* => .data.rel.ro.hot
.data.hot.* => .data.hot
...
```

https://github.com/llvm/llvm-project/pull/148985