* diagnostic.h (diagnostic_classification_change_t): New.
(diagnostic_context): Add history and push/pop list.
(diagnostic_push_diagnostics): Declare.
(diagnostic_pop_diagnostics): Declare.
* diagnostic.c (diagnostic_classify_diagnostic): Store changes
from pragmas in a history chain instead of the global table.
(diagnostic_push_diagnostics): New.
(diagnostic_pop_diagnostics): New.
(diagnostic_report_diagnostic): Scan history chain to find state
of diagnostics as of the diagnostic location.
* opts.c (set_option): Pass UNKNOWN_LOCATION to
diagnostic_classify_diagnostic.
(enable_warning_as_error): Likewise.
* diagnostic-core.h (DK_POP): Add after "real" diagnostics, for
use in the history chain.
* c-family/c-pragma.c (handle_pragma_diagnostic): Add push/pop,
allow these pragmas anywhere.
* doc/extend.texi: Document pragma GCC diagnostic changes.

* gcc.dg/pragma-diag-1.c: New.

From-SVN: r161115