> The ability to use a high-level, dynamic language (ObjC),
    > C, and even inline assembly in a single source file
    > is unique to Objective-C (at least among the
    > "mainstream" languages)[...]

Well Perl is mainstream enough to be installed on every *nix box, here's examples of assembly and C functions interoperating with Perl in the same source file: https://metacpan.org/pod/distribution/Inline-ASM/ASM.pod#SYN... & https://metacpan.org/pod/distribution/Inline-C/lib/Inline/C....

    > The "C ABI" (although there is no such thing)

Of course if you do this in Perl every one of your calls will need to go through a foreign function interface where Perl's structures are translated back & forth between its idea of datastructures and the OS's idea, avoiding that is what people really mean when they talk about the "C ABI".