Made Makefiles not override $CC and $CXX variables (needed for cross-compiling)

CppUnitLite/Makefile

@@ -4,9 +4,9 @@
 
 all: libCppUnitLite.a
 
-CC=gcc
-CXX=gcc
-CPP=gcc
+CC ?= gcc
+CXX ?= g++
+CPP ?= cpp
 CXXFLAGS += -O2
 
 sources = $(shell ls *.cpp)
@@ -32,4 +32,4 @@ install: all
 
 distclean: clean
 
-check: all
+check: all

colamd/Makefile

@@ -4,8 +4,8 @@
 
 all: libcolamd.a
 
-CC=gcc
-CXX=gcc
+CC ?= gcc
+CXX ?= g++
 CXXFLAGS += -O2
 CXXFLAGS += -fPIC
 

ldl/Makefile

@@ -9,7 +9,7 @@ include ./UFconfig.mk
 CXXFLAGS += -O2
 CXXFLAGS += -fPIC -I./
 
-CXX = g++
+CXX ?= g++
 
 all: demo
 

ldl/UFconfig.mk

@@ -33,7 +33,7 @@
 # C compiler and compiler flags:  These will normally not give you optimal
 # performance.  You should select the optimization parameters that are best
 # for your system.  On Linux, use "CFLAGS = -O3 -fexceptions" for example.
-CC = cc
+CC ?= cc
 # CFLAGS = -O   (for example; see below for details)
 
 # C++ compiler (also uses CFLAGS)