print-rtl: Fix printing of CONST_STRING in DEBUG_INSNs [PR93399]

print-rtl: Fix printing of CONST_STRING in DEBUG_INSNs [PR93399]

The following testcase fails to assemble, as CONST_STRING in the DEBUG_INSNs
is printed as is, so if it contains \n and/or \r, we are in trouble:
        .loc 1 14 3
        # DEBUG haystack => [si]
        # DEBUG needle => "
"
In the gimple dumps we print those (STRING_CSTs) as
  # DEBUG haystack => D#1
  # DEBUG needle => "\n"
so this patch uses what we use in tree printing for the CONST_STRINGs too.

2020-03-05  Jakub Jelinek  <jakub@redhat.com>

	PR middle-end/93399
	* tree-pretty-print.h (pretty_print_string): Declare.
	* tree-pretty-print.c (pretty_print_string): Remove forward
	declaration, no longer static.  Change nbytes parameter type
	from unsigned to size_t.
	* print-rtl.c (print_value) <case CONST_STRING>: Use
	pretty_print_string and for shrink way too long strings.

	* gcc.dg/pr93399.c: New test.