c++: suppress -Wdangling-reference for std::span [PR107532]

c++: suppress -Wdangling-reference for std::span [PR107532]

std::span is a view and therefore should be treated as a reference
wrapper class for the purposes of -Wdangling-reference.  I'm not sure
there's a pattern that we could check for.

	PR c++/107532

gcc/cp/ChangeLog:

	* call.cc (reference_like_class_p): Check for std::span.

gcc/testsuite/ChangeLog:

	* g++.dg/warn/Wdangling-reference10.C: New test.