/usr/src/gcc-4.8/debian/libgfortran3.symbols.64 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.
1 2 | _gfortran_clz128@GFORTRAN_1.2 4.4.0
_gfortran_ctz128@GFORTRAN_1.2 4.4.0
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