Update src/doc/rustc/src/platform-support/s390x-unknown-none-softfloat.md

Co-authored-by: Jubilee <workingjubilee@gmail.com>

Author: fneddy

src/doc/rustc/src/platform-support/s390x-unknown-none-softfloat.md

@@ -28,7 +28,8 @@ By default, code generated with the soft-float target should run on any Z System
 starting at [Z10][s390x-isa]. Enabling additional target features or changing the
 `-Ctarget-cpu` may raise the ISA required from the `z10` baseline.
 
-`extern "C"` does not use a stable ABI and is subject to change between llvm versions.
+`extern "C"` does not use a stable ABI and is subject to change between compiler
+or codegen backend versions.
 
 The target only generates object files in the ELF format. Any alternate formats
 or special considerations for binary layout will require linker options or linker