libdtrace: Format USDT symbols correctly based on symbol binding

Before we did not handle weak symbols correctly, sometimes resulting in
link errors from dtrace -G when processing object files where functions
with weak aliases contain USDT probes.

Reported by: rlibby
Sponsored by: The FreeBSD Foundation

(cherry picked from commit d00431a7bd0c4b4607943baed588e58ad5ae6150)