Added common recipe for building CMake projects. And added Catch2 recipe.

SConscript

@@ -206,6 +206,13 @@ env['UNITY_CACHE_DIR'] = Dir(f'{env["CACHE_DIR"]}/unity')
 env['BUILD_TYPE'] = build_type
 env.Append(LIBPATH = [env['LIB_DIR']]) # to allow submodules to link to each other without hassle
 
+# make sure these are all defined in case someone wants to use/copy them
+env.Append(CCFLAGS = [])
+env.Append(CXXFLAGS = [])
+env.Append(CPPPATH = [])
+env.Append(CPPDEFINES = [])
+env.Append(LINKFLAGS = [])
+
 # create the cache dir
 os.makedirs(env['CACHE_DIR'], exist_ok=True)
 cache_gitignore = f'{env["CACHE_DIR"]}/.gitignore'