Add set -eu to all shell scripts

These flags ensure that any errors cause the script to exit (instead of
just carrying on) (`-e`) and that any unrecognised substitution variables
cause an error instead of silently resolving to an empty string (`-u`).

Issues like Issue: google/ExoPlayer#10791 should be more quickly resolved with
`set -e` because the script will clearly fail with an error like
`make: command not found` which would give the user a clear pointer
towards the cause of the problem.

#minor-release

PiperOrigin-RevId: 490001419
(cherry picked from commit 45b8fb0ae1)

libraries/decoder_ffmpeg/src/main/jni/build_ffmpeg.sh

@@ -14,6 +14,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 #
+set -eu
 
 FFMPEG_MODULE_PATH=$1
 NDK_PATH=$2

libraries/decoder_opus/src/main/jni/convert_android_asm.sh

@@ -15,7 +15,7 @@
 # limitations under the License.
 #
 
-set -e
+set -eu
 ASM_CONVERTER="./libopus/celt/arm/arm2gnu.pl"
 
 if [[ ! -x "${ASM_CONVERTER}" ]]; then

libraries/decoder_vp9/src/main/jni/generate_libvpx_android_configs.sh

@@ -18,7 +18,7 @@
 # a bash script that generates the necessary config files for libvpx android ndk
 # builds.
 
-set -e
+set -eu
 
 if [ $# -ne 0 ]; then
   echo "Usage: ${0}"