Makefile improvements

• allow to build shared and static versions separately
• fix OSX shared build

Apparently for use in LALPulsar ResamplingOpenCL it's occasionally necessary to build a shared version of this library. This modification allows to build (and install) static and shared versions separately, and also fixes building the shared version on Mac OSX.

example/Makefile

@@ -5,7 +5,19 @@ CXX ?= g++
 
 TARGET = clfft_example
 
-CXXFLAGS += -O3 -Wall -g -I$(NVIDIA_SDK_INSTALL_PATH)/OpenCL/common/inc -I$(AMDAPPSDKROOT)/include -I../include
+ifndef OPENCL_INCLUDE
+ifdef CUDA_INSTALL_PATH
+OPENCL_INCLUDE = $(CUDA_INSTALL_PATH)/include
+endif
+ifdef OPENCL_INSTALL_PATH
+OPENCL_INCLUDE = $(OPENCL_INSTALL_PATH)/include
+endif
+endif
+ifndef OPENCL_INCLUDE
+OPENCL_INCLUDE = $(AMDAPPSDKROOT)/include -I$(NVIDIA_SDK_INSTALL_PATH)/OpenCL/common/inc
+endif
+
+CXXFLAGS += -O3 -Wall -g -I$(OPENCL_INCLUDE) -I../include -fPIC
 LDFLAGS += $(PWD)/../lib/libclfft.a
 
 OS = $(shell uname -s)