ipa: Make call redirection detect already adjusted calls (PR 93621)

PR 93621 testcase makes redirect_call_stmt_to_callee wrongly assume
that a call statement needs redirecting but then rightly fails an
assert ensuring the call statement parameters have not already been
adjusted because they were already created adjusted as part of thunk
expansion.

The test fails because the decl in the call call statement is
different than the decl of the callee, because the latter was created
in save_inline_function_body.  This patch adds a way to link these two
and detect the situation in redirect_call_stmt_to_callee.

2020-04-16  Martin Jambor  <mjambor@suse.cz>

	PR ipa/93621
	* ipa-inline.h (ipa_saved_clone_sources): Declare.
	* ipa-inline-transform.c (ipa_saved_clone_sources): New variable.
	(save_inline_function_body): Link the new body holder with the
	previous one.
	* cgraph.c: Include ipa-inline.h.
	(cgraph_edge::redirect_call_stmt_to_callee): Try to find the decl from
	the statement in ipa_saved_clone_sources.
	* cgraphunit.c: Include ipa-inline.h.
	(expand_all_functions): Free ipa_saved_clone_sources.

	testsuite/
	* g++.dg/ipa/pr93621.C: New test.