build MAINTENANCE improve messages in case of missing bison/flex

Fixes #254
Fixes #255

Author: rkrejci

CMakeLists.txt

@@ -21,9 +21,9 @@ find_package(BISON)
 find_program (SED_TOOL NAMES sed)
 
 if(NOT BISON_FOUND)
-	message(WARNING "Missing Bison.\nTarget bison does not exist.")
+	message(WARNING "Missing Bison.\nYou won't be able to generate source codes from changed flex/bison files.\nCompiling libyang should still works fine.")
 elseif (NOT FLEX_FOUND)
-	message(WARNING "Missing Flex.\nTarget bison does not exist.")
+	message(WARNING "Missing Flex.\nYou won't be able to generate source codes from changed flex/bison files.\nCompiling libyang should still works fine.")
 else()
 	if (BISON_VERSION VERSION_LESS 3)
 		set(EMPTYDIR "")