This is a strange regression whereby an enumeration type declared as
atomic (or volatile) incorrectly triggers the ODR machinery for its
values in LTO mode.
gcc/ada/
* gcc-interface/decl.c (gnat_to_gnu_entity): Build a TYPE_STUB_DECL
for the main variant of an enumeration type declared as volatile.
gcc/testsuite/
* gnat.dg/specs/lto25.ads: New test.