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.qt.include

@@ -357,6 +357,9 @@ qt_bitcoin_qt_LDADD += $(LIBBITCOIN_WALLET)
 endif
 qt_bitcoin_qt_LDADD += $(LIBBITCOIN_CLI) $(LIBBITCOIN_COMMON) $(LIBBITCOIN_UTIL) $(LIBBITCOIN_CRYPTO) $(LIBLEVELDB) $(LIBMEMENV) \
   $(BOOST_LIBS) $(QT_LIBS) $(QT_DBUS_LIBS) $(QR_LIBS) $(PROTOBUF_LIBS) $(BDB_LIBS)
+if USE_LIBSECP256K1
+  qt_bitcoin_qt_LDADD += secp256k1/libsecp256k1.la
+endif
 qt_bitcoin_qt_LDFLAGS = $(QT_LDFLAGS)
 
 #locale/foo.ts -> locale/foo.qm