checkpkg: Use read builtin to get new ".so" files

The read shell builtin is the proper way to read single lines. Also,
simplify grep(1) and awk(1) invocations and use a single awk(1)
expression, that supports extracting file names with spaces, instead.

Signed-off-by: Lukas Fleischer <archlinux@cryptocrack.de>
Signed-off-by: Pierre Schmitz <pierre@archlinux.de>