Change build_address_symbolic to return std::string
This changes two out parameters of build_address_symbolic to be
std::string, and updates the callers. This allows removing some
cleanups.
This patch also moves the declaration of build_address_symbolic out of
defs.h. I think that many things in defs.h should be elsewhere
instead. In this case, I moved the declaration to valprint.h, becuase
there is no "printcmd.h" -- but perhaps it would be better to
introduce that instead.
Tested by the buildbot.
gdb/ChangeLog
2018-06-07 Tom Tromey <tom@tromey.com>