Bugfix: Make USE_UPNP=- work with makefile.{linux-mingw,mingw,osx} too

src/makefile.linux-mingw

@@ -35,7 +35,10 @@ CFLAGS=-O2 -w -Wall -Wextra -Wformat -Wformat-security -Wno-unused-parameter $(D
 
 TESTDEFS = -DTEST_DATA_DIR=$(abspath test/data)
 
-ifdef USE_UPNP
+ifndef USE_UPNP
+	override USE_UPNP = -
+endif
+ifneq (${USE_UPNP}, -)
 	LIBPATHS += -L"$(DEPSDIR)/miniupnpc"
 	LIBS += -l miniupnpc -l iphlpapi
 	DEFS += -DSTATICLIB -DUSE_UPNP=$(USE_UPNP)

src/makefile.mingw

@@ -30,7 +30,10 @@ CFLAGS=-mthreads -O2 -w -Wall -Wextra -Wformat -Wformat-security -Wno-unused-par
 
 TESTDEFS = -DTEST_DATA_DIR=$(abspath test/data)
 
-ifdef USE_UPNP
+ifndef USE_UPNP
+	override USE_UPNP = -
+endif
+ifneq (${USE_UPNP}, -)
  INCLUDEPATHS += -I"C:\miniupnpc-1.6-mgw"
  LIBPATHS += -L"C:\miniupnpc-1.6-mgw"
  LIBS += -l miniupnpc -l iphlpapi

src/makefile.osx

@@ -97,7 +97,10 @@ OBJS= \
     obj/walletdb.o \
     obj/noui.o
 
-ifdef USE_UPNP
+ifndef USE_UPNP
+	override USE_UPNP = -
+endif
+ifneq (${USE_UPNP}, -)
 	DEFS += -DUSE_UPNP=$(USE_UPNP)
 ifdef STATIC
 	LIBS += $(DEPSDIR)/lib/libminiupnpc.a