Use ?= on compilers. Remove D_LINUX from client Makefile

cl_dll/Makefile

@@ -1,5 +1,5 @@
-CC=gcc
-CXX=g++
+CC?=gcc
+CXX?=g++
 SRCS+=../dlls/crossbow.cpp
 SRCS+=../dlls/crowbar.cpp
 SRCS+=../dlls/egon.cpp
@@ -67,7 +67,7 @@ SRCS+=./input_xash3d.cpp
 SRCS+=./scoreboard.cpp
 SRCS+=./MOTD.cpp
 INCLUDES =  -I../common -I. -I../game_shared -I../pm_shared -I../engine -I../dlls
-DEFINES = -Wno-write-strings -DLINUX -D_LINUX -Dstricmp=strcasecmp -D_strnicmp=strncasecmp -Dstrnicmp=strncasecmp -DCLIENT_WEAPONS -DCLIENT_DLL
+DEFINES = -Wno-write-strings -Dstricmp=strcasecmp -D_strnicmp=strncasecmp -Dstrnicmp=strncasecmp -DCLIENT_WEAPONS -DCLIENT_DLL
 CFLAGS = -m32
 OBJS = $(SRCS:.cpp=.o) $(SRCS_C:.c=.o)
 

dlls/Makefile

@@ -9,8 +9,8 @@ DLLNAME=hl
 ARCH=i386
 
 #make sure this is the correct compiler for your system
-CC=gcc
-CXX=g++
+CC?=gcc
+CXX?=g++
 
 DLL_SRCDIR=.
 ENGINE_SRCDIR=../engine