Disable strict pointer aliasing

I'm not really a C-level language lawyer, but the way how the code
routinely uses two differently-types pointers to access the same object
is undefined behavior in C. Just having "the same layout" of individual
struct members [does not make these types
compatible](https://en.cppreference.com/w/c/language/type#Compatible_types),
and that means that it is necessary to disable [strict
aliasing](https://en.cppreference.com/w/c/language/object#Strict_aliasing)
rules in the whole of libyang, as far as I can tell.

CMakeLists.txt

@@ -47,7 +47,7 @@ if(NOT CMAKE_BUILD_TYPE)
     set(CMAKE_BUILD_TYPE debug)
 endif()
 
-set(CMAKE_C_FLAGS         "${CMAKE_C_FLAGS} -Wall -Wextra -std=gnu99")
+set(CMAKE_C_FLAGS         "${CMAKE_C_FLAGS} -Wall -Wextra -std=gnu99 -fno-strict-aliasing")
 set(CMAKE_C_FLAGS_RELEASE "-O3 -DNDEBUG")
 set(CMAKE_C_FLAGS_PACKAGE "-g -O3 -DNDEBUG")
 set(CMAKE_C_FLAGS_DEBUG   "-g -Og")