Fix two regressions in scalar printing

Fix two regressions in scalar printing

PR gdb/21675 points out a few regressions in scalar printing.

One type of regression is due to not carrying over the old handling of
floating point printing -- where a format like "/d" causes a floating
point number to first be cast to a signed integer.  This patch restores
this behavior.

The other regression is a longstanding bug in print_octal_chars: one of
the constants was wrong.  This patch fixes the constant and adds static
asserts to help catch this sort of error.

ChangeLog
2017-08-14  Tom Tromey  <tom@tromey.com>

	PR gdb/21675
	* valprint.c (LOW_ZERO): Change value to 034.
	(print_octal_chars): Add static_asserts for octal constants.
	* printcmd.c (print_scalar_formatted): Add 'd' case.

testsuite/ChangeLog
2017-08-14  Tom Tromey  <tom@tromey.com>

	PR gdb/21675:
	* gdb.base/printcmds.exp (test_radices): New function.
	* gdb.dwarf2/var-access.exp: Use p/u, not p/d.
	* gdb.base/sizeof.exp (check_valueof): Use p/d.
	* lib/gdb.exp (get_integer_valueof): Use p/d.