c++: port to Sun C++ 5.12

The documentation for Oracle Solaris Studio 12.3 (Sun C++ 5.12
2011/11/16) says it supports C++03.  This compiler rejects the
location.cc use of std::max for some reason; I don’t know why
since I don’t use C++ as a rule.  The simplest workaround is to
open-code ‘max’.
* data/skeletons/location.cc (add_):
Do max by hand rather than relying on std::max.
Don’t include <algorithm.h>; no longer needed.

data/skeletons/location.cc

@@ -113,7 +113,7 @@ m4_define([b4_location_define],
     /// Compute max (min, lhs+rhs).
     static int add_ (int lhs, int rhs, int min)
     {
-      return std::max (min, lhs + rhs);
+      return lhs + rhs < min ? min : lhs + rhs;
     }
   };
 
@@ -345,7 +345,6 @@ m4_ifdef([b4_location_file], [[
 
 ]b4_cpp_guard_open([b4_location_path])[
 
-# include <algorithm> // std::max
 # include <iostream>
 # include <string>