common: one char arch shorthands, fail nicely on invalid arch

common

@@ -22,6 +22,24 @@ common_bench_cmd() (
 set_common_vars() {
   arch="$1"
   gem5="${2:-false}"
+  case "$arch" in
+    a|arm)
+      arch=arm
+      ;;
+    A|aarch64)
+      arch=aarch64
+      ;;
+    m|mips64)
+      arch=mips64
+      ;;
+    x|x86_64)
+      arch=x86_64
+      ;;
+    *)
+      printf "unknown arch: ${arch}\n" 1>&2
+      exit 2
+      ;;
+  esac
   common_suffix="${3:-}"
   buildroot_dir="${root_dir}/buildroot"
   arch_dir="$arch"