middle-end/110055 - avoid CLOBBERing static variables

The gimplifier can elide initialized constant automatic variables
to static storage in which case TARGET_EXPR gimplification needs
to avoid emitting a CLOBBER for them since their lifetime is no
longer limited.  Failing to do so causes spurious dangling-pointer
diagnostics on the added testcase for some targets.

	PR middle-end/110055
	* gimplify.cc (gimplify_target_expr): Do not emit
	CLOBBERs for variables which have static storage duration
	after gimplifying their initializers.

	* g++.dg/warn/Wdangling-pointer-pr110055.C: New testcase.

(cherry picked from commit 84eec291)