Back on this! It turn out that this breaks the shared Ada runtime.
Indeed, exported variables on Ada packages in a DLLs are only accessible
when linking against DLL (thanks to runtime pseudo reloc).
With the patch applied it is not possible to build any Ada application
using the shared runtime. This is a very serious problem, the patch
should be reverted.
Sorry for not having remembered before about this and why linking
against DLL was so important!
gpg --keyserver keys.gnupg.net --recv-key F949BD3B