Make all executables overridable

This is helpful for #119 which will add support for colorgcc

HISTORY.md

@@ -20,6 +20,7 @@ The following is the rough list of changes that went into different versions. I
 - Autodetect baudrate only if either a .ino/.pde is present
 - Allow building with Arduino core, without a .ino/.pde file
 - Ability to support different Arduino cores (https://github.com/sej7278)
+- Add support for colorgcc
 
 ### 0.12.0 (2013-06-20)
 - Fix "generated_assembly" target, which got broken earlier. Fix issue #76 (https://github.com/matthijskooijman)

arduino-mk/Arduino.mk

@@ -714,19 +714,19 @@ TARGETS    = $(OBJDIR)/$(TARGET).*
 CORE_LIB   = $(OBJDIR)/libcore.a
 
 # Names of executables
-CC      = $(AVR_TOOLS_PATH)/$(CC_NAME)
-CXX     = $(AVR_TOOLS_PATH)/$(CXX_NAME)
-AS      = $(AVR_TOOLS_PATH)/$(AS_NAME)
-OBJCOPY = $(AVR_TOOLS_PATH)/$(OBJCOPY_NAME)
-OBJDUMP = $(AVR_TOOLS_PATH)/$(OBJDUMP_NAME)
-AR      = $(AVR_TOOLS_PATH)/$(AR_NAME)
-SIZE    = $(AVR_TOOLS_PATH)/$(SIZE_NAME)
-NM      = $(AVR_TOOLS_PATH)/$(NM_NAME)
-REMOVE  = rm -rf
-MV      = mv -f
-CAT     = cat
-ECHO    = echo
-MKDIR   = mkdir -p
+CC      ?= $(AVR_TOOLS_PATH)/$(CC_NAME)
+CXX     ?= $(AVR_TOOLS_PATH)/$(CXX_NAME)
+AS      ?= $(AVR_TOOLS_PATH)/$(AS_NAME)
+OBJCOPY ?= $(AVR_TOOLS_PATH)/$(OBJCOPY_NAME)
+OBJDUMP ?= $(AVR_TOOLS_PATH)/$(OBJDUMP_NAME)
+AR      ?= $(AVR_TOOLS_PATH)/$(AR_NAME)
+SIZE    ?= $(AVR_TOOLS_PATH)/$(SIZE_NAME)
+NM      ?= $(AVR_TOOLS_PATH)/$(NM_NAME)
+REMOVE  ?= rm -rf
+MV      ?= mv -f
+CAT     ?= cat
+ECHO    ?= echo
+MKDIR   ?= mkdir -p
 
 # General arguments
 USER_LIBS      = $(wildcard $(patsubst %,$(USER_LIB_PATH)/%,$(ARDUINO_LIBS)))