/usr/src/gcc-4.8/debian/shlibs.commonn32 is in gcc-4.8-source 4.8.5-4ubuntu2.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
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libgcc_s 1 libn32gcc1 libstdc++ 6 libn32stdc++6