Fix type compatibility for types with flexible array member 1/2 [PR113688,PR114713...

Fix type compatibility for types with flexible array member 1/2 [PR113688,PR114713,PR117724]

Allow the TYPE_MODE of a type with an array as last member to differ from
another compatible type.

gcc/ChangeLog:
	* tree.cc (gimple_canonical_types_compatible_p): Add exception.
	(verify_type): Add exception.

gcc/lto/ChangeLog:
	* lto-common.cc (hash_canonical_type): Add exception.

(cherry picked from commit 1f48225a0ddfaf74a229105343b22f3086c4b8cb)