8066843: Messager.printMessage cannot print multiple errors for same source position
Summary: Using a DiagnosticFlag to mark diagnostics that should be always printed even if multiple of them have the same source position.
Reviewed-by: darcy, jjg, mcimadamore
TestMultipleErrors.java:41:8: compiler.err.proc.messager: error1
TestMultipleErrors.java:41:8: compiler.err.proc.messager: error2
TestMultipleErrors.java:41:8: compiler.err.proc.messager: error3
TestMultipleErrors.java:41:8: compiler.err.proc.messager: error4
4 errors