llvm-slicer: fix linkage type of declarations
llvm-slicer: fix linkage type of declarations

After slicing the function that are sliced thoroughtlhy
(thus are only a declaration now) may miss the linkage type
which break the IR.

Signed-off-by: Marek Chalupa <a05df156a69ad59faa9af9b666ef78009594c145@gmail.com>

mchalupa/dg,mchalupa/dg,mchalupa/dg,mchalupa/dg