Add Hash Padding Microbenchmarks

src/Makefile.bench.include

@@ -29,6 +29,7 @@ bench_bench_bitcoin_SOURCES = \
   bench/crypto_hash.cpp \
   bench/ccoins_caching.cpp \
   bench/gcs_filter.cpp \
+  bench/hashpadding.cpp \
   bench/merkle_root.cpp \
   bench/mempool_eviction.cpp \
   bench/mempool_stress.cpp \