/usr/src/gcc-4.8/debian/libitm1.symbols.64bit 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 3 4 | _ZGTtnam@LIBITM_1.0 4.7
_ZGTtnamRKSt9nothrow_t@LIBITM_1.0 4.7
_ZGTtnwm@LIBITM_1.0 4.7
_ZGTtnwmRKSt9nothrow_t@LIBITM_1.0 4.7
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