ossfuzz: add spng include dir to compiler flags

Author: concatime

tests/ossfuzz.sh

@@ -18,12 +18,14 @@ ar x libz.a
 ar rcs libspng_static.a *.o
 
 $CXX $CXXFLAGS -std=c++11 \
+    -I$SRC/libspng/spng \
     $SRC/libspng/tests/spng_read_fuzzer.c \
     -DSPNGT_HAVE_FMEMOPEN=1 \
     -o $OUT/spng_read_fuzzer \
     $LIB_FUZZING_ENGINE $SRC/libspng/build/libspng_static.a $SRC/zlib/build/libz.a
 
 $CXX $CXXFLAGS -std=c++11 -I$SRC/zlib/build -I$SRC/zlib \
+    -I$SRC/libspng/spng \
     $SRC/libspng/tests/spng_read_fuzzer.c \
     -DSPNGT_HAVE_FMEMOPEN=1 \
     -o $OUT/spng_read_fuzzer_structure_aware \