garray: Add support adding literal values

GArray's g_array_append_val(), g_array_prened_val() and g_array_insert_val() macros required an user to use literals to add a new value.

This could be inconvenient at times, but it's possible to avoid this with recent compilers, in fact in case glib_typeof is defined we can take advantage of it, to initialize a temporary variable to store the literal value and pass its address to the actual function.