secp256k1: Add build-side changes for libsecp256k1

Note: This is added to our existing automake targets rather than as a
libtool-style lib. The switch to libtool-style targets can come later if it
proves to not add any complications.

src/Makefile.test.include

@@ -69,6 +69,11 @@ test_test_bitcoin_LDADD = $(LIBBITCOIN_SERVER) $(LIBBITCOIN_CLI) $(LIBBITCOIN_CO
 if ENABLE_WALLET
 test_test_bitcoin_LDADD += $(LIBBITCOIN_WALLET)
 endif
+
+if USE_LIBSECP256K1
+  test_test_bitcoin_LDADD += secp256k1/libsecp256k1.la
+endif
+
 test_test_bitcoin_LDADD += $(BDB_LIBS)
 
 nodist_test_test_bitcoin_SOURCES = $(GENERATED_TEST_FILES)