riscv64: -march=rv64gcv1p0 vs riscv_vector.h

[Mathieu Malaterre via Gcc-help <gcc-help@xxxxxxxxxxx>]

Hi all,

I see that GCC-12 now accepts `-march=rv64gcv1p0` but at the same time
does not provide a header file for <riscv_vector.h>.

Could someone please confirm this is a known issue ?

Thanks