build_environment: blosc build fixes.

blosc embedded a copy of zlib/pthreads causing duplicate symbol linker errors. pthreads was windows specific, but zlib may apply to other platforms as well.

build_files/build_environment/cmake/blosc.cmake

@@ -28,12 +28,20 @@ set(BLOSC_EXTRA_ARGS
 	-DDEACTIVATE_SNAPPY=ON
 )
 
+if(WIN32)
+	#prevent blosc from including it's own local copy of zlib in the object file
+	#and cause linker errors with everybody else
+	set(BLOSC_EXTRA_ARGS ${BLOSC_EXTRA_ARGS}
+		-DPREFER_EXTERNAL_ZLIB=ON
+	)
+endif()
+
 ExternalProject_Add(external_blosc
 	URL ${BLOSC_URI}
 	DOWNLOAD_DIR ${DOWNLOAD_DIR}
 	URL_HASH MD5=${BLOSC_HASH}
 	PREFIX ${BUILD_DIR}/blosc
-	#PATCH_COMMAND ${PATCH_CMD} --verbose -p 1 -N -d ${BUILD_DIR}/blosc/src/external_blosc < ${PATCH_DIR}/blosc.diff
+	PATCH_COMMAND ${PATCH_CMD} --verbose -p 1 -N -d ${BUILD_DIR}/blosc/src/external_blosc < ${PATCH_DIR}/blosc.diff
 	CMAKE_ARGS -DCMAKE_INSTALL_PREFIX=${LIBDIR}/blosc ${DEFAULT_CMAKE_FLAGS} ${BLOSC_EXTRA_ARGS}
 	INSTALL_DIR ${LIBDIR}/blosc
 )