fix link failure with libtiff

The fuzz targets were failing to link with:

```
Step google#4: /work/lib/libtiff.a(tif_lzma.o): In function `TIFFInitLZMA':
Step google#4: /src/libtiff/libtiff/tif_lzma.c:465: undefined reference to
`lzma_lzma_preset'
```

It looks like it's become necessary to explicitly link -llzma, see:

https://gitlab.com/libtiff/libtiff/commit/4159bda6db2f8cf8e848d8095b5d37d49ba67a10

oss-fuzz issue:

https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=18928#c4

Thanks to @lovell.

projects/libvips/build.sh

@@ -128,7 +128,7 @@ for fuzzer in fuzz/*_fuzzer.cc; do
  $WORK/lib/libtiff.a \
  $LIB_FUZZING_ENGINE \
  -Wl,-Bstatic \
- -lfftw3 -lgmodule-2.0 -lgobject-2.0 -lffi -lglib-2.0 -lpcre -lexpat \
+ -lfftw3 -lgmodule-2.0 -lgobject-2.0 -lffi -lglib-2.0 -lpcre -lexpat -llzma \
  -Wl,-Bdynamic -pthread
  ln -sf "seed_corpus.zip" "$OUT/${target}_seed_corpus.zip"
 done