/usr/src/gcc-4.9/debian/lib32quadmath0.symbols is in gcc-4.9-source 4.9.3-13ubuntu2.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 | libquadmath.so.0 lib32quadmath0 #MINVER#
#include "libquadmath0.symbols.common"
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