Fix error message for invalid command line opts

When a command line option is not recognized, the error message across
our build scripts would indirectly dereference OPTIND. This is incorrect
and likely to result in an unbound variable exception.

Replace with printing '-${OPTARG}'.

Change-Id: I191645b876c0bd32a29758d1ac7c31c9a5b7f6b3
diff --git a/aarch64/run_gdb.sh b/aarch64/run_gdb.sh
index 2555d13..6210c8a 100755
--- a/aarch64/run_gdb.sh
+++ b/aarch64/run_gdb.sh
@@ -42,7 +42,7 @@
 		exit 0
 		;;
 	\?)
-		echo "Invalid option: ${!OPTIND}" 1>&2
+		echo "Invalid option: -${OPTARG}" 1>&2
 		usage 1>&2
 		exit 1
 		;;
diff --git a/aarch64/run_qemu.sh b/aarch64/run_qemu.sh
index d628518..58d7b5a 100755
--- a/aarch64/run_qemu.sh
+++ b/aarch64/run_qemu.sh
@@ -130,7 +130,7 @@
 		exit 0
 		;;
 	\?)
-		echo "Invalid option: ${!OPTIND}" 1>&2
+		echo "Invalid option: -${OPTARG}" 1>&2
 		usage 1>&2
 		exit 1
 		;;
diff --git a/kvm-unit-tests/run_test.sh b/kvm-unit-tests/run_test.sh
index b38d5cc..3f5a95f 100755
--- a/kvm-unit-tests/run_test.sh
+++ b/kvm-unit-tests/run_test.sh
@@ -68,7 +68,7 @@
 		exit 0
 		;;
 	\?)
-		echo "Invalid option: ${!OPTIND}" 1>&2
+		echo "Invalid option: -${OPTARG}" 1>&2
 		usage 1>&2
 		exit 1
 		;;