[lld] [lld][macho] Support order cstrings with -order_file_cstring (PR #140307)

[via llvm-commits]

SharonXSharon wrote:

@ellishg 
> The format of -order_file already allows for prefixes depending on the platform and object file.
> I think we could extend this to support the literal prefix <cstr>:. 

do you mean we should accept format like 
```
arm64:file_name1:symbol1
file_name2:symbol2
symbol3
cstr:0x111
cstr:file_name4:0x222
```
where the first prefix is `cpu_type|"cstr":`? 
or do you mean we prepend an optional "cstr:", so that we can accept
`cstr:arm64:file_name1:0x222`

https://github.com/llvm/llvm-project/pull/140307