opus: improve build performance

Before:
```
opus: Compile times: Vanilla=185; Replay=67;
```

After:
```
opus: Compile times: Vanilla=95; Replay=21;
```

Signed-off-by: David Korczynski <david@adalogics.com>

Author: DavidKorczynski

projects/opus/build.sh

@@ -20,6 +20,7 @@ FUZZERS="opus_encode_fuzzer opus_multistream_decode_fuzzer opus_multistream_enco
 BUILDS=(floating fixed floating_qext fixed_qext)
 
 tar xvf $SRC/opus_testvectors.tar.gz
+zip -r $SRC/zipped-corpus.zip opus_testvectors/
 
 if [[ $CFLAGS = *sanitize=memory* ]]; then
   CFLAGS+=" -D_FORTIFY_SOURCE=0"
@@ -64,6 +65,6 @@ for build in "${BUILDS[@]}"; do
     # fuzzer's name
     [ -f tests/$fuzzer.options ] \
         && cp tests/$fuzzer.options $OUT/${fuzzer}_${build}.options
-    zip -r $OUT/${fuzzer}_${build}_seed_corpus.zip opus_testvectors/
+    cp $SRC/zipped-corpus.zip $OUT/${fuzzer}_${build}_seed_corpus.zip
   done
 done