x86-dregs: Print debug registers one per line

x86-dregs: Print debug registers one per line

This get around this warning given by clang...

  /home/emaisin/src/binutils-gdb/gdb/nat/x86-dregs.c:209:7: error: variable 'i' is incremented both in the loop header and in the loop body [-Werror,-Wfor-loop-analysis]
        i++;
        ^
  /home/emaisin/src/binutils-gdb/gdb/nat/x86-dregs.c:199:32: note: incremented here
    ALL_DEBUG_ADDRESS_REGISTERS (i)
                               ^

... I decided in the end to simply print the debug registers one per
line.  I don't think it particularly helps readability to have them two
per line anyway.

gdb/ChangeLog:

	* nat/x86-dregs.c (x86_show_dr): Print registers one per line.