Replace GCC 4.8 toolchain with GCC 5

cmake/gcc-4.8.cmake → cmake/gcc-5.cmake

@@ -1,5 +1,5 @@
-set(CMAKE_C_COMPILER gcc-4.8)
-set(CMAKE_CXX_COMPILER g++-4.8)
+set(CMAKE_C_COMPILER gcc-5)
+set(CMAKE_CXX_COMPILER g++-5)
 set(CMAKE_CXX_STANDARD 11)
 set(CMAKE_CXX_STANDARD_REQUIRED True)
 set(CMAKE_CXX_EXTENSIONS Off)