Auto merge of #6531 - mmatyas:arm_build2, r=metajack

Allow to override CXX and AR for cross compilation.

**Update:** Please see issue #6537 

Required by some ARM patches.

Part of #6327

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ports/gonk/makefile.cargo

@@ -1,7 +1,7 @@
-ifeq (androideabi,$(findstring androideabi,$(TARGET)))
+ifeq (eabi,$(findstring eabi,$(TARGET)))
 
-CXX := $(TARGET)-g++
-AR := $(TARGET)-ar
+CXX ?= $(TARGET)-g++
+AR ?= $(TARGET)-ar
 CFLAGS := -fPIC -O2
 
 else