riscv: riscv-cores.def: Add T-Head XuanTie C906
This adds T-Head's XuanTie C906 to the list of known cores as "thead-c906".
The C906 is shipped for quite some time (it is the core of the Allwinner D1).
Note, that the tuning struct for the C906 is already part of GCC (it is
also name "thead-c906").
gcc/ChangeLog:
* config/riscv/riscv-cores.def (RISCV_CORE): Add "thead-c906".
gcc/testsuite/ChangeLog:
* gcc.target/riscv/mcpu-thead-c906.c: New test.
Signed-off-by: Christoph Müllner <christoph.muellner@vrull.eu>