Use $(CC) and $(CXX) instead of hardcoding gcc and g++.
Remove include and library paths we don't want.
Include externally-supplied CFLAGS, CXXFLAGS, CPPFLAGS, LDFLAGS.

Subverting make's ability to build in parallel is still terrible but I
don't want to spend much more time fixing this ancient software.
--- Makefile.orig	2007-07-06 17:46:11.000000000 -0500
+++ Makefile	2020-08-20 04:02:11.000000000 -0500
@@ -8,31 +8,32 @@
 #
 
 
-# LINUX and BSD CFLAGS
-CFLAGS = -O3 -I/usr/include/pcap -I/usr/local/include/pcap  -I./ -L/usr/lib/libsocket.so  -g -L/opt/csw/lib -ggdb
+# LINUX and BSD CFLAGS AND CXXFLAGS
+CFLAGS := -O3 -g -ggdb -I. $(CPPFLAGS) $(CFLAGS)
+CXXFLAGS := -O3 -g -ggdb -I. $(CPPFLAGS) $(CXXFLAGS)
 
-# LINUX  LFLAGS
-LFLAGS = -lresolv -lnsl -lpcap -L/usr/lib/libpcap.so.0.6.2
+# LINUX LFLAGS
+LFLAGS := -lresolv -lnsl -lpcap $(LDFLAGS)
 
 # BSD BFLAGS
-BFLAGS = -lpcap -L/usr/lib/libpcap.so
+BFLAGS := -lpcap $(LDFLAGS)
 
 
 final : sancp.cc Makefile
-	g++ -Wall $(CFLAGS) -c build_acl.cc -o build_acl.o
-	g++ -Wall $(CFLAGS) -c misc_functs.cc -o misc_functs.o
-	g++ -Wall $(CFLAGS) -c outputFileHandle.cc -o outputFileHandle.o
-	g++ -Wall $(CFLAGS) -c apply_rule.cc -o apply_rule.o
-	g++ -Wall $(CFLAGS) -c decode.cc -o decode.o
-	g++ -Wall $(CFLAGS) -c fileHandle.cc -o fileHandle.o
-	g++ -Wall $(CFLAGS) -c MemoryPool.cc -o MemoryPool.o
-	g++ -Wall $(CFLAGS) -c pcapFileHandle.cc -o pcapFileHandle.o
-	g++ -Wall $(CFLAGS) -c sancp.cc -o sancp.o
-	gcc -Wall $(CFLAGS) -c pcap_functions.c -o pcap_functions.o
-	g++ -Wall $(CFLAGS) -c permissions.cc -o permissions.o
-	g++ -Wall $(CFLAGS) -c check_packet.cc -o check_packet.o
-	g++ -Wall $(CFLAGS) -c statefull_logging.cc -o statefull_logging.o
-	g++ -Wall $(CFLAGS) -c help.cc -o help.o
+	$(CXX) -Wall $(CXXFLAGS) -c build_acl.cc -o build_acl.o
+	$(CXX) -Wall $(CXXFLAGS) -c misc_functs.cc -o misc_functs.o
+	$(CXX) -Wall $(CXXFLAGS) -c outputFileHandle.cc -o outputFileHandle.o
+	$(CXX) -Wall $(CXXFLAGS) -c apply_rule.cc -o apply_rule.o
+	$(CXX) -Wall $(CXXFLAGS) -c decode.cc -o decode.o
+	$(CXX) -Wall $(CXXFLAGS) -c fileHandle.cc -o fileHandle.o
+	$(CXX) -Wall $(CXXFLAGS) -c MemoryPool.cc -o MemoryPool.o
+	$(CXX) -Wall $(CXXFLAGS) -c pcapFileHandle.cc -o pcapFileHandle.o
+	$(CXX) -Wall $(CXXFLAGS) -c sancp.cc -o sancp.o
+	$(CC) -Wall $(CFLAGS) -c pcap_functions.c -o pcap_functions.o
+	$(CXX) -Wall $(CXXFLAGS) -c permissions.cc -o permissions.o
+	$(CXX) -Wall $(CXXFLAGS) -c check_packet.cc -o check_packet.o
+	$(CXX) -Wall $(CXXFLAGS) -c statefull_logging.cc -o statefull_logging.o
+	$(CXX) -Wall $(CXXFLAGS) -c help.cc -o help.o
 
 clean :
 	@(echo "" > platform.h)
@@ -41,10 +42,10 @@
 bsd :
 	@(echo "#define PLATFORM_BSD" > platform.h)
 	@make final
-	g++ -Wall $(BFLAGS) $(CFLAGS) -o sancp sancp.o  misc_functs.o check_packet.o statefull_logging.o build_acl.o apply_rule.o decode.o pcap_functions.o pcapFileHandle.o fileHandle.o MemoryPool.o permissions.o outputFileHandle.o help.o
+	$(CXX) -Wall $(BFLAGS) $(CXXFLAGS) -o sancp sancp.o misc_functs.o check_packet.o statefull_logging.o build_acl.o apply_rule.o decode.o pcap_functions.o pcapFileHandle.o fileHandle.o MemoryPool.o permissions.o outputFileHandle.o help.o
 
 linux :
 	@(echo "#define PLATFORM_LINUX" > platform.h)
 	@make final
-	g++ -Wall $(LFLAGS) $(CFLAGS) -o sancp sancp.o misc_functs.o check_packet.o statefull_logging.o build_acl.o apply_rule.o decode.o pcap_functions.o pcapFileHandle.o fileHandle.o MemoryPool.o permissions.o outputFileHandle.o help.o
+	$(CXX) -Wall $(LFLAGS) $(CXXFLAGS) -o sancp sancp.o misc_functs.o check_packet.o statefull_logging.o build_acl.o apply_rule.o decode.o pcap_functions.o pcapFileHandle.o fileHandle.o MemoryPool.o permissions.o outputFileHandle.o help.o