Cause of regression 6387

[Wolfgang Bangerth]

> How about `-gdwaf -g1'?

Close. The switch was to dwarf2. -gdwarf -g1 works before and after that 
change, -gdwarf-2 -g1 does not work before or after the change. So I'll at 
this to flags and run it again. (Sorry for not noticing it before, I tried 
-gdwarf-2 alone, but did not realize that it is necessary to use -g1 as 
well...)

Regards
  Wolfgang

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Wolfgang Bangerth              email:           bangerth@ticam.utexas.edu
                               www: http://www.ticam.utexas.edu/~bangerth