[doc] Note variable shadowing at max macro using statement expression

[doc] Note variable shadowing at max macro using statement expression

When suggesting to rewrite the unsafe (with respect to multiple evaluation of
arguments) macro definition:
...
  #define max(a,b) ((a) > (b) ? (a) : (b))
...
into the safe macro definition:
...
  #define maxint(a,b) \
    ({int _a = (a), _b = (b); _a > _b ? _a : _b; })
...
mention the variable shadowing problem for:
...
  #define maxint3(a, b, c) \
    ({int _a = (a), _b = (b), _c = (c); maxint (maxint (_a, _b), _c); })
...

2019-04-11  Tom de Vries  <tdevries@suse.de>

	* doc/extend.texi (@node Statement Exprs): Note variable shadowing at
	max macro using statement expression.

From-SVN: r270287