doc: Fixes to RTL-SSA sample code

doc: Fixes to RTL-SSA sample code

This patch fixes up the code examples in the RTL-SSA documentation (the
sections on making insn changes) to reflect the current API.

The main issues are as follows:
 - rtl_ssa::recog takes an obstack_watermark & as the first parameter.
   Presumably this is intended to be the change attempt, so I've updated
   the examples to pass this through.
 - The variants of recog and restrict_movement that take an ignore
   predicate have been renamed with an _ignoring suffix, so I've
   updated callers to use those names.
 - A couple of minor "obvious" fixes to add a missing address-of
   operator and correct a variable name.

gcc/ChangeLog:

	* doc/rtl.texi: Fix up sample code for RTL-SSA insn changes.