Don't stomp on build flags (#635)

Let CMake handle the default optimizations for various configurations. We don't need to override them. In fact, overriding them makes it impossible for users to override them themselves.

CMakeLists.txt

@@ -159,11 +159,6 @@ if(CMAKE_CXX_COMPILER_ID MATCHES "GNU" OR
 		set(CMAKE_BUILD_TYPE Release)
 	endif()
 	#
-	set(CMAKE_CXX_FLAGS_RELEASE "-O2")
-	set(CMAKE_CXX_FLAGS_RELWITHDEBINFO "-O2 -g")
-	set(CMAKE_CXX_FLAGS_DEBUG "-g")
-	set(CMAKE_CXX_FLAGS_MINSIZEREL "-Os")
-	#
 	set(GCC_EXTRA_OPTIONS "")
 	#
 	if(BUILD_SHARED_LIBS)