message: [Build] Set complete cpp/cxx flags for bench_pivx binary
  Follows suit with the rest of our binary targets and prevents a
  relocation error when linking on some architectures.
diff: @@ -15,7 +15,8 @@ bench_bench_pivx_SOURCES = \
  bench/perf.h \
  bench/prevector_destructor.cpp
  -bench_bench_pivx_CPPFLAGS = $(BITCOIN_INCLUDES) $(EVENT_CLFAGS) $(EVENT_PTHREADS_CFLAGS) -I$(builddir)/bench/
  +bench_bench_pivx_CPPFLAGS = $(AM_CPPFLAGS) $(BITCOIN_INCLUDES) $(EVENT_CFLAGS) $(EVENT_PTHREADS_CFLAGS) -I$(builddir)/bench/
  +bench_bench_pivx_CXXFLAGS = $(AM_CXXFLAGS) $(PIE_FLAGS)
  bench_bench_pivx_LDADD = \
  $(LIBBITCOIN_SERVER) \
  $(LIBBITCOIN_COMMON) \
  