gallium: silence __builtin_frame_address nonzero argument is unsafe warning

gallium: silence __builtin_frame_address nonzero argument is unsafe warning

Calling __builtin_frame_address with a nonzero argument is unsafe
but is sometimes done for debugging purposes. Since this code is
part of some debug util code I'm assuming that is the case here
and using GCC pragma to silence the warning.

Reviewed-by: Jose Fonseca <jfonseca@vmware.com>