[lld] [LLD][ELF][RISCV][Zicfilp] Handle .note.gnu.property sections for Zicfilp/Zicfiss features (PR #127193)

[Fangrui Song via llvm-commits]

MaskRay wrote:

The first three paragraphs are dense but probably not so clear. Can you replace that with:

```
* When all relocatable files contain a `.note.gnu.property` section (with `NT_GNU_PROPERTY_TYPE_0` notes) containing the `GNU_PROPERTY_RISCV_FEATURE_1_GCS` bit, or if `-z zicfiss=always` is specified:
  + The output file will contain a `.note.gnu.property` section with the bit set.
  + A `PT_GNU_PROPERTY` program header is created to encompass the `.note.gnu.property` section.
* If `-z zicfiss-report={warning,error}` is specified, the linker will report a warning or error for any relocatable file lacking the feature bit.
```

https://github.com/llvm/llvm-project/pull/127193