RISC-V: Introduce XTheadVector as a subset of V1.0.0
This patch is to introduce basic XTheadVector support
(march string parsing and a test for __riscv_xtheadvector)
according to https://github.com/T-head-Semi/thead-extension-spec/
gcc/ChangeLog:
* common/config/riscv/riscv-common.cc
(riscv_subset_list::parse): Add new vendor extension.
* config/riscv/riscv-c.cc (riscv_cpu_cpp_builtins):
Add test marco.
* config/riscv/riscv.opt: Add new mask.
gcc/testsuite/ChangeLog:
* gcc.target/riscv/predef-__riscv_th_v_intrinsic.c: New test.
* gcc.target/riscv/rvv/xtheadvector.c: New test.
Co-authored-by: Jin Ma <jinma@linux.alibaba.com>
Co-authored-by: Xianmiao Qu <cooper.qu@linux.alibaba.com>
Co-authored-by: Christoph Müllner <christoph.muellner@vrull.eu>