honor CXXFLAGS/LDFLAGS

Index: Makefile
--- Makefile.orig
+++ Makefile
@@ -33,6 +33,9 @@ linux32:
 linux64:
 	$(CXX) $(SRC) $(CPP_FLAGS) ${STEAM_LIB}/linux64/libsteam_api.so -o $(GNU_OUT) -shared -fPIC $(GNU_FLAGS)
 
+openbsd:
+	$(CXX) $(SRC) $(CPP_FLAGS) $(CXXFLAGS) $(LDFLAGS) -o $(GNU_OUT) -shared -fPIC $(GNU_FLAGS)
+
 ifeq ($(OS),Windows_NT)
 # Windows stuff
 SHELL=cmd
