The minimal compiler version, GCC 4.9 supports this flag.

Nathan Chancellor pointed out:
 "This flag is technically ignored by clang (see commit
 05b0798916f01690b5903302e51f3136274e291f) but that obviously
 does not matter for the sake of this."

Here is the godbolt:
https://godbolt.org/z/59cK6oSigned-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nathan Chancellor <natechancellor@gmail.com>