build: At least honor the LDFLAGS from the environment

When not honoring the environment we end up linking it without the
GNU_HASH for symbol look-up. Put the content into LIBS and place
these options last to make it link.

We still override the CFLAGS but that seems to not cause issues yet

Fixes:

ERROR: ... No GNU_HASH in the elf binary: 'rtl8168-eeprom' [ldflags]

Makefile

@@ -1,11 +1,11 @@
 CFLAGS=-Wall -g `pkg-config --cflags libpci`
-LDFLAGS=`pkg-config --libs libpci`
+LIBS=`pkg-config --libs libpci`
 
 %.o: %.c
 	$(CC) $(CFLAGS) -o $@ -c $^
 
 rtl8168-eeprom: rtl8168-eeprom.o
-	$(CC) $(LDFLAGS) -o $@ $^
+	$(CC) -o $@ $^ $(LDFLAGS) $(LIBS)
 
 clean:
 	rm -f rtl8168-eeprom rtl8168-eeprom.o