thunk3.C, thunk4.C: Gate on dg-require-weak.

	* g++.dg/abi/thunk3.C, g++.dg/abi/thunk4.C: Gate on
	dg-require-weak.  Adjust regexp to handle leading-underscore
	targets, NO_DOT_IN_LABEL targets and space as well as TAB after
	.weak.

From-SVN: r109286