testsuite: add coverage for diagnostics relating to inlining (PR tree-optimization...

testsuite: add coverage for diagnostics relating to inlining (PR tree-optimization/83336)

In theory, the diagnostics subsystem can print context information on
code inlining when diagnostics are emitted by the middle-end, describing
the chain of inlined callsites that led to a particular warning,
but PR tree-optimization/83336 describes various issues with this.

An underlying issue is that we have very little automated testing for
this code: gcc.dg/tm/pr52141.c has a test, but in general, prune.exp
filters out the various "inlined from" lines.

The following patch adds test coverage for it for C and C++ via a new
testsuite plugin, which emits a warning from the middle-end; the test
cases use dg-regexp to verify that the "inlined from" lines are
emitted correctly, with the correct function names and source locations.

Doing so requires a change to prune.exp: the dg-regexp lines have to
be handled *before* the "inlined from" lines are stripped.

gcc/testsuite/ChangeLog:
	PR tree-optimization/83336
	* g++.dg/cpp0x/missing-initializer_list-include.C: Update for
	changes to prune.exp's handling of dg-regexp.
	* g++.dg/plugin/diagnostic-test-inlining-1.C: New test case.
	* g++.dg/plugin/plugin.exp (plugin_test_list): Add it, via
	gcc.dg's plugin/diagnostic_plugin_test_inlining.c.
	* gcc.dg/plugin/diagnostic-test-inlining-1.c: New test case.
	* gcc.dg/plugin/diagnostic-test-inlining-2.c: Likewise.
	* gcc.dg/plugin/diagnostic-test-inlining-3.c: Likewise.
	* gcc.dg/plugin/diagnostic-test-inlining-4.c: Likewise.
	* gcc.dg/plugin/diagnostic_plugin_test_inlining.c: New test
	plugin.
	* gcc.dg/plugin/plugin.exp (plugin_test_list): Add them.
	* lib/prune.exp (prune_gcc_output): Move call to handle-dg-regexps
	to before the various text stripping regsup invocations,
	in particular, to before the stripping of "inlined from".

From-SVN: r255786