Add the `--{no-}separate-cstring-literal-sections` option to emit
cstring literals into sections defined by their section name. This
allows for changes like swiftlang/swift#84300
and swiftlang/swift#84236 to actually have an
affect. The default behavior has not changed.

The reason this is useful is because strings in different sections might
have different access patterns at runtime. By splitting these strings
into separate sections, we may reduce the number of page faults during
startup. For example, the ObjC runtime accesses all strings in
`__objc_classname` before main.

…8720)

Add the `--{no-}separate-cstring-literal-sections` option to emit
cstring literals into sections defined by their section name. This
allows for changes like swiftlang/swift#84300
and swiftlang/swift#84236 to actually have an
affect. The default behavior has not changed.

The reason this is useful is because strings in different sections might
have different access patterns at runtime. By splitting these strings
into separate sections, we may reduce the number of page faults during
startup. For example, the ObjC runtime accesses all strings in
`__objc_classname` before main.

Clang emits ObjC strings into special sections

https://github.com/llvm/llvm-project/blob/d5e7c27d53887e6ae490d8e26193a54987728458/clang/lib/CodeGen/CGObjCMac.cpp#L4056-L4072

As far as I can tell from `CGObjCMac.cpp`:
* types go into `__objc_methtype`
* class, category, and protocol names go into `__objc_classname`
* method names, property names, and property types go into
`__objc_methname`

See also #84236.