aarch64: bugfix when finding 1st bfd input with GNU property

aarch64: bugfix when finding 1st bfd input with GNU property

The current implementation of searching the first input BFD with GNU
properties has a bug. The search was not filtering on object inputs
belonging to the output link unit only, but was also including dynamic
objects, BFD plugins, and linker-created files.
This means that the initial initialization of the output properties
were skewed, and warnings on input files that should have been emitted
were not.

This patch fixes the filtering to exclude the object input files not
belonging to the output link unit, not having the same ELF class, and
not the same target architecture.