Makefile: improve selection of possible include paths

src/Makefile

@@ -6,7 +6,22 @@ AR ?= ar
 TARGET = libeclfft.a
 TARGET2 = libeclfft.so
 
-CXXFLAGS += -O3 -Wall -g -I$(NVIDIA_SDK_INSTALL_PATH)/OpenCL/common/inc -I$(AMDAPPSDKROOT)/include -I../include -fPIC
+ifndef OPENCL_INCLUDE
+ifdef AMDAPPSDKROOT
+OPENCL_INCLUDE = $(AMDAPPSDKROOT)/include
+endif
+ifdef NVIDIA_SDK_INSTALL_PATH
+OPENCL_INCLUDE = $(NVIDIA_SDK_INSTALL_PATH)/OpenCL/common/inc
+endif
+ifdef CUDA_INSTALL_PATH
+OPENCL_INCLUDE = $(CUDA_INSTALL_PATH)/include
+endif
+ifdef OPENCL_INSTALL_PATH
+OPENCL_INCLUDE = $(OPENCL_INSTALL_PATH)/include
+endif
+endif
+
+CXXFLAGS += -O3 -Wall -g -I$(OPENCL_INCLUDE) -I../include -fPIC
 OS = $(shell uname -s)
 ifeq ($(OS), Darwin)
 	CXXFLAGS += -I/System/Library/Frameworks