analyzer: don't print the duplicate count by default

analyzer: don't print the duplicate count by default

The note about duplicates attached to analyzer diagnostics feels like an
implementation detail; it's likely just noise from the perspective of an
end-user.

This patch disables it by default, introducing a flag to re-enable it.

gcc/analyzer/ChangeLog:
	* analyzer.opt (fanalyzer-show-duplicate-count): New option.
	* diagnostic-manager.cc
	(diagnostic_manager::emit_saved_diagnostic): Use the above to
	guard the printing of the duplicate count.

gcc/ChangeLog:
	* doc/invoke.texi (-fanalyzer-show-duplicate-count): New.

gcc/testsuite/ChangeLog:
	* gcc.dg/analyzer/CVE-2005-1689-dedupe-issue.c: Add
	-fanalyzer-show-duplicate-count.