ci: add riscv32 ci

Author: inkydragon

.github/workflows/cross.yml

@@ -28,6 +28,7 @@ jobs:
           # Builds successfully, but tests fail.
           # - { arch: mips64,   triple: mips64-linux-gnuabi64 }
           # - { arch: mips64el, triple: mips64el-linux-gnuabi64 }
+          - { arch: riscv32,  triple: riscv32-linux-gnu }
           - { arch: riscv64,  triple: riscv64-linux-gnu }
           - { arch: s390x,    triple: s390x-linux-gnu }
     env: