btrace: work around _dl_runtime_resolve returning to resolved function

btrace: work around _dl_runtime_resolve returning to resolved function

On some systems, _dl_runtime_resolve returns to the resolved function
instead of jumping to it.  Since btrace will not find the function in
the current stack back trace, it will start a new back trace on the
same level.  It will look the same to the user via the backtrace
command but the frames will have different id's which confuses stepping.

This fixes a test fail with 32-bit inferior reported by Jan Kratochvil.

gdb/
	* btrace.c (ftrace_update_function): Treat return as tailcall for
	"_dl_runtime_resolve".