ipa/119973 - IPA PTA issue with global initializers

ipa/119973 - IPA PTA issue with global initializers

For global initializers with IPA PTA we initialize them from the
IPA reference data but that lacks references to the constant pool.
The following conservatively considers the whole initializer.

	PR ipa/119973
	* tree-ssa-structalias.cc (create_variable_info_for):
	Build constraints from DECL_INITIAL directly rather than
	the IPA reference list which is incomplete.

	* gcc.dg/torture/pr119973.c: New testcase.

(cherry picked from commit 7a16ef443b13fff9537baa533597836c57131262)