Remove some unnecessary backslashes

Remove some unnecessary backslashes

I found a couple of unnecessary backslashes in gdb.  This removes
them.

Offhand, I wonder whether this abstract_to_concrete thing could be
done some other way?  This seems possibly expensive.

Anyway, tested by rebuilding.  I'm going to check this in as obvious.

gdb/ChangeLog
2019-11-27  Tom Tromey  <tromey@adacore.com>

	* dwarf2read.h (struct dwarf2_per_objfile): Remove unnecessary
	backslashes.
	* cp-support.c: Remove unnecessary backslashes.

Change-Id: I956c91ae24407eeafec8a731545b45f5222e6a9d