Bump sentencepiece C++ standard from 11 to 17 (#13221)

Author: ZacharyGarrett

projects/sentencepiece/build.sh

@@ -25,7 +25,7 @@ make install
 # build fuzzers
 for fuzzer in $(find $SRC -name '*_fuzzer.cc'); do
   fuzz_basename=$(basename -s .cc $fuzzer)
-  $CXX $CXXFLAGS -std=c++11 -I. -I$SRC/sentencepiece \
+  $CXX $CXXFLAGS -std=c++17 -I. -I$SRC/sentencepiece \
       -I$SRC/sentencepiece/src \
       -I$SRC/sentencepiece/src/builtin_pb/ \
       -I$SRC/sentencepiece/third_party/protobuf-lite/ \