construct no longer supports automatic conversion from char* to std::string

[Braden McDaniel <braden@…>]

Given:

foo {
  explicit foo(const std::string &);
};

...this use of boost::phoenix::construct now fails in Boost 1.63.0 (using Apple Clang 8.0):

boost::phoenix::construct<foo>("str");

The issue can be worked around by explicitly constructing a std::string:

boost::phoenix::construct<foo>(std::string{"str"});

...however, the automatic conversion from char* worked in Boost 1.62.0.

[Nikita Kniazev <nok.raven@…>]

This is problem in C++11 interface.

Should be fixed in ​https://github.com/boostorg/phoenix/pull/58