message: Fix accidentally remove warning as error flag
diff: @@ -472,8 +472,8 @@ libbitcoin_util_a_SOURCES = \
  crypto/MerkleTreeProof/merkle-tree.cpp \
  $(BITCOIN_CORE_H)
  -libsigma_a_CPPFLAGS = $(AM_CPPFLAGS) $(BITCOIN_INCLUDES)
  -libsigma_a_CXXFLAGS = $(AM_CXXFLAGS) $(PIE_FLAGS)
  +libsigma_a_CPPFLAGS = $(AM_CPPFLAGS) $(BITCOIN_INCLUDES) -Werror
  +libsigma_a_CXXFLAGS = $(AM_CXXFLAGS) $(PIE_FLAGS) -Werror
  libsigma_a_SOURCES = \
  sigma/r1_proof.h \
  sigma/r1_proof_generator.h \
  