d: Fix SEGV in hash_table<odr_name_hasher, false, xcallocator>::find_slot_with_hash

d: Fix SEGV in hash_table<odr_name_hasher, false, xcallocator>::find_slot_with_hash

This patch fixes LTO bug with the D front-end.  As DECL_ASSEMBLER_NAME
is set on the TYPE_DECL, so TYPE_CXX_ODR_P must also be set on the type.

The addition of merge_aggregate_types is not strictly needed now, but it
fixes a problem introduced in newer versions of the dmd front-end where
templated types could be sent more than once to the D code generator.

gcc/d/ChangeLog:

2020-03-20  Iain Buclaw  <ibuclaw@gdcproject.org>

	PR lto/91027
	* d-tree.h (struct GTY): Add daggregate field.
	(IDENTIFIER_DAGGREGATE): Define.
	(d_mangle_decl): Add declaration.
	* decl.cc (mangle_decl): Remove static linkage, rename to...
	(d_mangle_decl): ...this, update all callers.
	* types.cc (merge_aggregate_types): New function.
	(TypeVisitor::visit (TypeStruct *)): Call merge_aggregate_types, set
	IDENTIFIER_DAGGREGATE and TYPE_CXX_ODR_P.
	(TypeVisitor::visit (TypeClass *)): Likewise.