[PR111497][LRA]: Copy substituted equivalence

When we substitute the equivalence and it becomes shared, we can fail
to correctly update reg info used by LRA.  This can result in wrong
code generation, e.g. because of incorrect live analysis.  It can also
result in compiler crash as the pseudo survives RA.  This is what
exactly happened for the PR.  This patch solves this problem by
unsharing substituted equivalences.

gcc/ChangeLog:

	PR middle-end/111497
	* lra-constraints.cc (lra_constraints): Copy substituted
	equivalence.
	* lra.cc (lra): Change comment for calling unshare_all_rtl_again.

gcc/testsuite/ChangeLog:

	PR middle-end/111497
	* g++.target/i386/pr111497.C: new test.