Not add initialization for variables been initialized by FEs [PR102359]

Not add initialization for variables been initialized by FEs [PR102359]

C++ FE creates proxy variables, which have associated DECL_VALUE_EXPR
and have been initialized by FE. For such auto variable, we should not
add initialization when -ftrivial-auto-var-init presents.

	PR middle-end/102359

gcc/ChangeLog:

2021-10-05  qing zhao  <qing.zhao@oracle.com>

	* gimplify.c (gimplify_decl_expr): Not add initialization for an
	auto variable when it has been initialized by frontend.

gcc/testsuite/ChangeLog:

2021-10-05  qing zhao  <qing.zhao@oracle.com>

	* g++.dg/pr102359_1.C: New test.
	* g++.dg/pr102359_2.C: New test.