build: quit abusing LIBS for Windows builds.

Similar to the INCLUDES changes in 6b099402b4, split out LIBS into individual
entries for more fine-grained control.

Also add MINIUPNPC_LIBS which was missing before, and hook it up to
executables.

src/Makefile.am

@@ -281,7 +281,7 @@ if TARGET_WINDOWS
 bitcoind_SOURCES += bitcoind-res.rc
 endif
 
-bitcoind_LDADD += $(BOOST_LIBS) $(BDB_LIBS) $(SSL_LIBS) $(CRYPTO_LIBS)
+bitcoind_LDADD += $(BOOST_LIBS) $(BDB_LIBS) $(SSL_LIBS) $(CRYPTO_LIBS) $(MINIUPNPC_LIBS)
 bitcoind_CPPFLAGS = $(BITCOIN_INCLUDES)
 bitcoind_LDFLAGS = $(RELDFLAGS) $(AM_LDFLAGS)
 
@@ -293,7 +293,8 @@ bitcoin_cli_LDADD = \
   $(LIBBITCOIN_CRYPTO) \
   $(BOOST_LIBS) \
   $(SSL_LIBS) \
-  $(CRYPTO_LIBS)
+  $(CRYPTO_LIBS) \
+  $(MINIUPNPC_LIBS)
 
 bitcoin_cli_SOURCES = \
   bitcoin-cli.cpp
@@ -317,7 +318,9 @@ endif
 
   bitcoin_tx_LDADD += $(BOOST_LIBS) \
   $(SSL_LIBS) \
-  $(CRYPTO_LIBS)
+  $(CRYPTO_LIBS) \
+  $(MINIUPNPC_LIBS)
+
 bitcoin_tx_SOURCES = bitcoin-tx.cpp
 bitcoin_tx_CPPFLAGS = $(BITCOIN_INCLUDES)
 #