[Bug bootstrap/97183] zstd build failure for gcc 10 on Ubuntu 16.04

[rguenth at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97183

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
I think amending the configure test for the specific macro / API uses is better
than a version check.