merge PortSpec env into each output env

core/deps.mk

@@ -375,7 +375,7 @@ define dep_autopatch_rebar.erl
 					"%.o: %.C\n\t$$\(CXX) -c -o $$\@ $$\< $$\(CXXFLAGS) $$\(ERL_CFLAGS) $$\(DRV_CFLAGS) $$\(EXE_CFLAGS)\n\n",
 					"%.o: %.cc\n\t$$\(CXX) -c -o $$\@ $$\< $$\(CXXFLAGS) $$\(ERL_CFLAGS) $$\(DRV_CFLAGS) $$\(EXE_CFLAGS)\n\n",
 					"%.o: %.cpp\n\t$$\(CXX) -c -o $$\@ $$\< $$\(CXXFLAGS) $$\(ERL_CFLAGS) $$\(DRV_CFLAGS) $$\(EXE_CFLAGS)\n\n",
-					[[Output, ": ", K, " = ", ShellToMk(V), "\n"] || {K, V} <- lists:reverse(MergeEnv(FilterEnv(Env)))],
+					[[Output, ": ", K, " += ", ShellToMk(V), "\n"] || {K, V} <- lists:reverse(MergeEnv(FilterEnv(Env)))],
 					Output, ": $$\(foreach ext,.c .C .cc .cpp,",
 						"$$\(patsubst %$$\(ext),%.o,$$\(filter %$$\(ext),$$\(wildcard", Input, "))))\n",
 					"\t$$\(CC) -o $$\@ $$\? $$\(LDFLAGS) $$\(ERL_LDFLAGS) $$\(DRV_LDFLAGS) $$\(EXE_LDFLAGS)",