Bug#856274: removal of ada-gcc-name patch causes build failures for non default gnat builds

[Nicolas Boulenguez]

Package: gnat-5,gnat-6,gnat-7
Followup-For: Bug #856274

On gnat-7/7.1.0-7,  the work-around has no effect.
ARCH-gcc-7-7 is searched but not found.