Recent versions (> 5.33) of `file` report liblto_plugin.so as
executable:

 $ file liblto_plugin.so
 liblto_plugin.so.0.0.0: ELF 64-bit LSB pie executable ...

Which then leads to improper packaging of the plugin, resulting in the
broken compiler:

 configure: checking whether the C compiler works
 mips-openwrt-linux-musl/bin/ld: liblto_plugin.so: error loading plugin: liblto_plugin.so: invalid ELF header

As the LTO compiler plugin library is incorrectly packaged as SDK
executable:

 $ head -1 ~/staging_dir/toolchain...libexec/gcc/.../liblto_plugin.so
 #!/usr/bin/env bash

Fix this by filtering out shared libraries from the patching.

Ref: https://bugzilla.redhat.com/show_bug.cgi?id=1296868


Acked-by: Jo-Philipp Wich <jo@mein.io>
Signed-off-by: Petr Štetiar <ynezz@true.cz>