Use SFML 2.6's set of compiler warnings

Some minor tweaks were made to remove Android-specific workarounds
that CSFML doesn't need and removing a few warnings that are not
feasible to fix at the moment.

cmake/Macros.cmake

@@ -1,4 +1,5 @@
 include(CMakeParseArguments)
+include(${PROJECT_SOURCE_DIR}/cmake/CompilerWarnings.cmake)
 
 # add a new target which is a CSFML library
 # ex: csfml_add_library(csfml-graphics
@@ -15,6 +16,9 @@ macro(csfml_add_library target)
     # add the CSFML header path
     target_include_directories(${target} PUBLIC ${PROJECT_SOURCE_DIR}/include)
 
+    # add warnings
+    set_file_warnings(${THIS_SOURCES})
+
     # define the export symbol of the module
     string(REPLACE "-" "_" NAME_UPPER "${target}")
     string(TOUPPER "${NAME_UPPER}" NAME_UPPER)