https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82641
--- Comment #2 from Richard Earnshaw <rearnsha at gcc dot gnu.org> --- ARMv8-a is the only architecture variant where the CRC extension is optional. In later variants it is enabled by default; in earlier versions of the architecture it doesn't exist. Your report lacks a testcase we can use to examine this more fully.
