Enable v extension on riscv

Author: calebzulawski

.github/workflows/ci.yml

@@ -188,7 +188,7 @@ jobs:
         include:
           - { target: powerpc64-unknown-linux-gnu, target_feature: "+vsx" }
           - { target: powerpc64le-unknown-linux-gnu, target_feature: "+vsx" }
-          - { target: riscv64gc-unknown-linux-gnu, target_feature: "+zvl128b" }
+          - { target: riscv64gc-unknown-linux-gnu, target_feature: "+v,+zvl128b" }
 
     steps:
       - uses: actions/checkout@v2