Fix substitution of carriage return on Darwin.

Fix substitution of carriage return on Darwin.

* lib/autoconf/status.m4 (_AC_OUTPUT_FILES_PREPARE): Set
ac_cs_awk_cr to '\\r', so that sed portably expands this to '\r'
rather than a literal carriage return, to fix substitution on
Darwin.  Regression introduced in 2.63b.
Report by Peter O'Gorman.

Signed-off-by: Ralf Wildenhues <Ralf.Wildenhues@gmx.de>