/usr/src/gcc-7/debian/libquadmath.symbols is in gcc-7-source 7.3.0-16ubuntu3.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 | libquadmath.so.0 #PACKAGE# #MINVER#
(symver)QUADMATH_1.0 4.6
(symver)QUADMATH_1.1 6
|